My guess is that there is a conflict in your routes.
You must have a route like this somewhere:
Route::get('/appraisal_respondents/{appraisal_respondent}', 'AppraisalRespondentsController@show');
When you go to the URL /appraisal_respondents/msf_manager, it is handled by this route.
Indeed, the error says: "No query results for model [App\Models\Appraisal\AppraisalRespondent] msf_manager"
So, it's like msf_manager is considered like an id for route model binding and there's obviously no id with a value of msf_manager.
I would suggest you to move your route to the top to test. I am talking about this one:
Route::get('/appraisal_respondents/msf_manager', 'AppraisalRespondentsController@msf_manager')->name('appraisal_respondents.msf_manager');
In reality, it just have to be above the first one I mentioned.