As of yesterday (June 13) we have EXACTLY the same issue...
Have tried various things like duplicating the screen. Nothing we have tried seems to fix the data source connection to SharePoint, it is broken...
We noticed there was a PowerApps update recently. Not sure if it is related to this issue, but it does feel like too much of a coincidence to be totally unrelated.
This worked absolutely fine previously. It is not a complicated app, it is a very simple form connected to a very simple list. The data source is to a very simple custom list in SharePoint. We were creating a custom form to enhance the user experience when submitting new items, using radio button controls.
We are NOT using experimental features. The only preview feature being used is "components".
The one thing we did notice is the new setting under the (overall) app settings, under "advanced settings". The new experience for data sources was switched on, but we do not recall if that was something we did at the beginning or it was done after the upgrade. For sure WE did NOT change it recently. That seems to require that all data sources are removed and replaced before being used. Could be the upgrade switched that on?
Anyway, we are VERY UNHAPPY to say that switching that new experience for data sources off and trying to recreate the data source - ALSO DOES NOT WORK. No matter what we do, it seems the only response we get from trying to connect to our Sharepoint is "The request was not sent or there was no response from the server. Check your internet connection."
Could be another coincidence, but ... Now the app does not show on the list of apps in the main power apps "my apps" or "org apps" list.
So this issue does NOT appear to relate to our power app. This issue seems to be something to do with data sources connecting to SharePoint......
Have tried this with other lists, SAME issue.
Now just tried to create a simple test list from scratch, and have an issue with that also! We can create the list, but when we try to access the list settings we get a screen that simply says, "Error - file not found"???!