This has been reported before, but I'll post it again here, since this was not fixed in the last patch.
If you play for a longer time, then the in-game chat virtual keyboard (how you can type with your controller) doesn't work anymore. The only way to fix this is to restart ESO completely (hard-quit the game, then relaunch).
When this happens is random, but most of the time this happens if you're inside ESO, send a xbox message via xbox itself (and used that other virtual keyboard) and then get back into ESO.
The keyboard just won't pop-up anymore, as if it was removed from the game.
Please fix this, this is game-breaking, people need to be able to communicate with each other!!