@William_Simetin-Gren, here's the reply I received from Pebble support:
From the description you have provided, it sounds like there may be an issue with the app cache on your iPhone.
To correct this, could you uninstall, then re-install the Pebble app on your iPhone?
Please note, this will mean losing the Pebble Health data on your phone.
This should correct the issue you are experiencing, but if it does not, please let us know and we will be sure to assist you further.
I followed these instructions and my Pebble app is now 68.6 MB. I did lose my health data, but any data that I had synced with Apple HealthKit is retained in the iOS Health app. My watchfaces and watchapps remained installed and reappeared after reinstalling the Pebble Time app. The biggest downside is that I did have to reset watch app settings and my notification settings in the Pebble Time app.