I'm running Mendix on-premise and have a few Microflows for Administrative purposes that take more than a couple of minutes to run. I use a Blocking pop-up on the button. I receive a generic Error after a couple of minutes (I haven't checked for exact timing), but I can see that the MF is still running properly and will finish without error on the server console. Could this be a webpage timeout setting or something else that causes this generic error? Using debugger = no errors, Server Log = No Errors
I thik this might be a timeout of your browser, check the browser console, it should specifiy the error.
The synchronous MF calls timeout by default after a couple minutes. They don't stop running but users won't see the results if you're displaying a page afterwards.
You can try setting it to run asynchronously in the MF settings, or run it in the background with the Community commons "executeMicroflowInBackground" java action.