After subscribing, only the cancel button. After cancelling no subcription options

Dear sparkers,

I've had an issue with Spark and Laravel 5.4 which I thought could be fixed after updating to 5.5. The problem is that after subscribing to a plan only the CANCEL button is available. No options to start another plan. If I press the CANCEL button, the whole subscription page is empty. If I press F12, i have the following 2 errors:

app.js:42273 [Vue warn]: Error in render function: "TypeError: Cannot read property 'name' of undefined"

found in

---> <SparkResumeSubscription>
      <SparkSubscription>
        <SparkSettings>
          <Root>

warn @ app.js:42273
app.js:42360 TypeError: Cannot read property 'name' of undefined
   at Proxy.render (eval at createFunction (app.js:51714), <anonymous>:2:35887)
   at VueComponent.Vue._render (app.js:45981)
   at VueComponent.updateComponent (app.js:44369)
   at Watcher.get (app.js:44710)
   at new Watcher (app.js:44699)
   at mountComponent (app.js:44373)
   at VueComponent.Vue$3.$mount (app.js:49763)
   at VueComponent.Vue$3.$mount (app.js:51953)
   at init (app.js:45352)
   at createComponent (app.js:46994)

To see if it persists in Laravel 5.5 & Spark, I first created a vanilla Spark website and added the Stripe credentials. I fixed the subscription plan ids to the ones from Stripe and everything worked fine. I could start a subscription, cancel it and resume after cancelling.

I next tried to incrementally copy my files to the new page. I tried to test as soon as I implemented a small update. However, some of the single copy actions required quite a lot of downstream copy actions. After a while, I stumbled across the same problem as before. So I am running out of options.

Anyone else have an idea how to tackle this?

Thanks in advance,