I had some trouble awhile ago but after logging back in on my computer the phone app corrected itself.
I usually just recommend that people use the forum in their browser on Android phones, as Tapatalk's app is severely lacking in comparison to the iOS app. The forum is fully responsive and mobile-friendly
Delete the App and switch off the device and do a hard re-start, then off to App Store and re-install (remember it will show "get" from the cloud) had something similar with my iPad, Oh, remember to note down any of your "subscribed" threads so as not to lose them