@v-micsh-msftMany thanks for your the follow up with this issue. MS Support told us last week that the issue will self-resolved so I guess that powerapp upgrade was the root cause. I have checked the problematic app and everything seems to be ok.
This issue can also occur when a connection to a 3rd party plugin is made in Flow and PowerApps and your API-key is expired. This happened to me when using Pdf4Me and Muhimbi PDF trial versions. Removing the connections from in your connection list and removing the connections from the PowerApps and Flow itself solves the issue.