Hi,
I couldn't share the access since it's working behind a vpn.
Also, I didn't find the time for testing in the meantime. However 'good news'. It's now working again.
Nothing changed on server side. I had to reinstall Enpass (again) on the Android phone and voila.
Can't tell what it was, but I still _assume_ it was something that was caused by Enpass itself.
"Case closed".