PHP Upgrade from 5.* to 7.1 Error

Good day,

After my upgrade I am now receiving the following error where it was working before. Please help me here :)

Error:

ErrorException in Jobcard.php line 106:
A non well formed numeric value encountered

Line 106:

            $percentage_downtime = $this->down_time / $secondsRunning * 100;        

More Code

    public function getDownTimePercentageAttribute() {
        $date_start = new Carbon($this->date_start_actual);
        $secondsRunning = $date_start::now()->diffInSeconds($date_start);

        if ($secondsRunning === 0 || $secondsRunning === null) {
            $percentage_downtime = 0;
        }else{
            $percentage_downtime = $this->down_time / $secondsRunning * 100;        
        }
        return $percentage_downtime; // . " Seconds Running = " . $secondsRunning . "  Down Time = " . $this->down_time;
    }

Rest of the Error:

in Jobcard.php line 106
at HandleExceptions->handleError('8', 'A non well formed numeric value encountered', 'C:\laragon\www\prodx\app\Jobcard.php', '106', array('date_start' => object(Carbon), 'secondsRunning' => '33458')) in Jobcard.php line 106
at Jobcard->getDownTimePercentageAttribute(null) in Model.php line 2752
at Model->mutateAttribute('downtime_percentage', null) in Model.php line 2654
at Model->getAttributeValue('downtime_percentage') in Model.php line 2634
at Model->getAttribute('downtime_percentage') in Model.php line 3429
at Model->__get('downtime_percentage') in ProductionController.php line 364
at ProductionController->getPerformance('74')
at call_user_func_array(array(object(ProductionController), 'getPerformance'), array('jobcard_id' => '74')) in Controller.php line 80
at Controller->callAction('getPerformance', array('jobcard_id' => '74')) in ControllerDispatcher.php line 146
at ControllerDispatcher->call(object(ProductionController), object(Route), 'getPerformance') in ControllerDispatcher.php line 94
at ControllerDispatcher->Illuminate\Routing\{closure}(object(Request))
at call_user_func(object(Closure), object(Request)) in Pipeline.php line 52
at Pipeline->Illuminate\Routing\{closure}(object(Request))
at call_user_func(object(Closure), object(Request)) in Pipeline.php line 102
at Pipeline->then(object(Closure)) in ControllerDispatcher.php line 96
at ControllerDispatcher->callWithinStack(object(ProductionController), object(Route), object(Request), 'getPerformance') in ControllerDispatcher.php line 54
at ControllerDispatcher->dispatch(object(Route), object(Request), 'App\Http\Controllers\ProductionController', 'getPerformance') in Route.php line 174
at Route->runController(object(Request)) in Route.php line 140
at Route->run(object(Request)) in Router.php line 724
at Router->Illuminate\Routing\{closure}(object(Request))
at call_user_func(object(Closure), object(Request)) in Pipeline.php line 52
at Pipeline->Illuminate\Routing\{closure}(object(Request)) in RoleMiddleware.php line 20
at RoleMiddleware->handle(object(Request), object(Closure), 'sysadmin', 'compadmin', 'shiftman', 'qualityop', 'machineop')
at call_user_func_array(array(object(RoleMiddleware), 'handle'), array(object(Request), object(Closure), 'sysadmin', 'compadmin', 'shiftman', 'qualityop', 'machineop')) in Pipeline.php line 136
at Pipeline->Illuminate\Pipeline\{closure}(object(Request))
at call_user_func(object(Closure), object(Request)) in Pipeline.php line 32
at Pipeline->Illuminate\Routing\{closure}(object(Request)) in RevalidateBackHistory.php line 19
at RevalidateBackHistory->handle(object(Request), object(Closure))
at call_user_func_array(array(object(RevalidateBackHistory), 'handle'), array(object(Request), object(Closure))) in Pipeline.php line 136
at Pipeline->Illuminate\Pipeline\{closure}(object(Request))
at call_user_func(object(Closure), object(Request)) in Pipeline.php line 32
at Pipeline->Illuminate\Routing\{closure}(object(Request)) in Authenticate.php line 28
at Authenticate->handle(object(Request), object(Closure))
at call_user_func_array(array(object(Authenticate), 'handle'), array(object(Request), object(Closure))) in Pipeline.php line 136
at Pipeline->Illuminate\Pipeline\{closure}(object(Request))
at call_user_func(object(Closure), object(Request)) in Pipeline.php line 32
at Pipeline->Illuminate\Routing\{closure}(object(Request)) in VerifyCsrfToken.php line 64
at VerifyCsrfToken->handle(object(Request), object(Closure))
at call_user_func_array(array(object(VerifyCsrfToken), 'handle'), array(object(Request), object(Closure))) in Pipeline.php line 136
at Pipeline->Illuminate\Pipeline\{closure}(object(Request))
at call_user_func(object(Closure), object(Request)) in Pipeline.php line 32
at Pipeline->Illuminate\Routing\{closure}(object(Request)) in ShareErrorsFromSession.php line 49
at ShareErrorsFromSession->handle(object(Request), object(Closure))
at call_user_func_array(array(object(ShareErrorsFromSession), 'handle'), array(object(Request), object(Closure))) in Pipeline.php line 136
at Pipeline->Illuminate\Pipeline\{closure}(object(Request))
at call_user_func(object(Closure), object(Request)) in Pipeline.php line 32
at Pipeline->Illuminate\Routing\{closure}(object(Request)) in StartSession.php line 64
at StartSession->handle(object(Request), object(Closure))
at call_user_func_array(array(object(StartSession), 'handle'), array(object(Request), object(Closure))) in Pipeline.php line 136
at Pipeline->Illuminate\Pipeline\{closure}(object(Request))
at call_user_func(object(Closure), object(Request)) in Pipeline.php line 32
at Pipeline->Illuminate\Routing\{closure}(object(Request)) in AddQueuedCookiesToResponse.php line 37
at AddQueuedCookiesToResponse->handle(object(Request), object(Closure))
at call_user_func_array(array(object(AddQueuedCookiesToResponse), 'handle'), array(object(Request), object(Closure))) in Pipeline.php line 136
at Pipeline->Illuminate\Pipeline\{closure}(object(Request))
at call_user_func(object(Closure), object(Request)) in Pipeline.php line 32
at Pipeline->Illuminate\Routing\{closure}(object(Request)) in EncryptCookies.php line 59
at EncryptCookies->handle(object(Request), object(Closure))
at call_user_func_array(array(object(EncryptCookies), 'handle'), array(object(Request), object(Closure))) in Pipeline.php line 136
at Pipeline->Illuminate\Pipeline\{closure}(object(Request))
at call_user_func(object(Closure), object(Request)) in Pipeline.php line 32
at Pipeline->Illuminate\Routing\{closure}(object(Request))
at call_user_func(object(Closure), object(Request)) in Pipeline.php line 102
at Pipeline->then(object(Closure)) in Router.php line 726
at Router->runRouteWithinStack(object(Route), object(Request)) in Router.php line 699
at Router->dispatchToRoute(object(Request)) in Router.php line 675
at Router->dispatch(object(Request)) in Kernel.php line 246
at Kernel->Illuminate\Foundation\Http\{closure}(object(Request))
at call_user_func(object(Closure), object(Request)) in Pipeline.php line 52
at Pipeline->Illuminate\Routing\{closure}(object(Request)) in MainMiddleware.php line 25
at MainMiddleware->handle(object(Request), object(Closure))
at call_user_func_array(array(object(MainMiddleware), 'handle'), array(object(Request), object(Closure))) in Pipeline.php line 136
at Pipeline->Illuminate\Pipeline\{closure}(object(Request))
at call_user_func(object(Closure), object(Request)) in Pipeline.php line 32
at Pipeline->Illuminate\Routing\{closure}(object(Request)) in CheckForMaintenanceMode.php line 44
at CheckForMaintenanceMode->handle(object(Request), object(Closure))
at call_user_func_array(array(object(CheckForMaintenanceMode), 'handle'), array(object(Request), object(Closure))) in Pipeline.php line 136
at Pipeline->Illuminate\Pipeline\{closure}(object(Request))
at call_user_func(object(Closure), object(Request)) in Pipeline.php line 32
at Pipeline->Illuminate\Routing\{closure}(object(Request))
at call_user_func(object(Closure), object(Request)) in Pipeline.php line 102
at Pipeline->then(object(Closure)) in Kernel.php line 132
at Kernel->sendRequestThroughRouter(object(Request)) in Kernel.php line 99
at Kernel->handle(object(Request)) in index.php line 53