Forgive me if this should have been in the app forum, but it feels like troubleshooting more to me.
Factory Droid 4 user who hasn't had any problems until tonight when Gmail app stopped working properly.
Synch appears to be okay. I can push email to the app from outside sources and from gmail itself. I can make changes through a pc browser and through the phone browser and everything shows up as changed. Gmail works properly in phone browser.
The menu button in the gmail app does not work, nor does the account and folder links at the top.
Pressing a message has no effect. Starring may briefly work once.
While running, the screen occasionally flashes to black then back to the inbox.
All other apps, including Google apps like G+, YouTube, etc. appear to be working correctly. Sharing to Gmail causes a force close, however.
Have powered down.
Have cleared cache and app data.