ADE “Not responding” to epubs exported from InDesign

I primarily use ADE as the default app for opening epubs upon their initial export from InDesign, in order to quickly check that they are exporting correctly. It has always functioned in this capacity with no problems. As of last week it will no longer open epubs that I export from InDesign: neither newly created epubs, nor prior existing epubs that have previously opened in ADE with no problems. Now, ADE just prompts “Not Responding” and I have to kill the process from the Task Manager to stop it.

ADE still opens 3rd party commercial epubs without problem, which seems to isolate the problem to the file being exported from InDesign, rather than with ADE. However, to reiterate, this problem is affecting old files that ADE has always opened in the past, in addition to files newly exported from InDesign that have passed EpubCheck validation.

I’m on Windows 10. I have uninstalled ADE ad re-installed a fresh version—no help.

I assume I’m missing something simple. Has anyone else come across this?

Thank you.