Error on opening app in Edit mode: Unable to process binding "style... | Contract failure: Unspecified

[Pjweij]

Today on trying to open any of my PowerApps using the Experimental feature: "Formula-level error management" in Edit mode give me the following error on startup and then nothing is loaded on the screen.

"An error occured while opening the file"



Reverting back to a previous version or exporting & Importing the PowerApp does not solve the problem.

Apps without the experimental feature turned off are working just fine. Luckily I can still 'Play' the affected PowerApps..

Any ideas? Please help...

Update: 
With the use of : 

Contracts.checkNumberOrNull = function(){}

I can turn the Experimental feature off, save and publish the app. This breaks the Play mode and does not resolve the issue..

[Pjweij]

https://powerusers.microsoft.com/t5/General-Discussion/Can-no-longer-edit-one-of-my-PowerApps/td-p/2...
Tried this.. it makes it possible to Edit the app and turn the Experimental feature off.

However after then saving, publishing and opening the app in Edit Mode the normal way.. the error returns

[v-monli-msft]

Hi @Pjweij ,

By default, when you create an app, the  "Formula-level error management" should be off. I just tested by turing it on and save it, then I am able to reopen it in edit mode successfully. Having all Experimental features sections switches turned off is the baseline and safest way to run your app and this should not break the Play mode.

May I know the reason why you need this turn this feature on for this app?

Regards,

Mona

[Pjweij · Accepted solution]

Hi Mona,

Thanks for your reply, unfortunatly I am unable to tell you. My predecessor who has left the company initially created these apps ans apparantly turned the features on.

Through the weekend I have tried and finally found the cause of the error. The error had nothing to do with a feature and everything with an formule beeing used to determine a Font size. We are using an Config Screen where the default font size is written in a label. Every other label is then pointed to this config label.
Apparantly, some labels had a formula like:
lblFontSize.Size-5
And this broke the entire app, as in the Fontsize UI dropdown, you would see the value  '17-5'  instead of the actual outcome.

In my opinion this should not result in beeing unable to Edit the app, but at least we found a solution. We are also unable to reproduce the issue in new apps