So you’re saying, the “Mobile” (app) version does not work on the mobile device, but the “Desktop” via a browser works fine, on the same mobile device?

Yes on the same mobile device.
Whenever I use the tablet, before absolutely anything, I click on Safari app, or Chrome app, it gives me Google, I search for Fluther.com, (not iFluther) Fluther.com mobile version shows up by default, most of the time. Signing in hasn’t been a problem either way, Mobile version or Desktop version (except a few months ago when everyone was having a problem posting a question (OP) and a few other things) But on the day that I posted this question I coudn’t sign in on the Mobile version. I tried a few times. I switched to Desktop, no problem.