I will premise this bug report with: I believe binds will not stick (save between sessions) if the ESO client is improperly shut down so this bug report has nothing to do with that scenario.
When I play this game, and I'd like to note I have just returned to playing ESO recently, keybinds I have set many sessions ago simply become unbound. I haven't changed anything *aside* from resetting the the keybindings that mysteriously become unbound. No idea how to make this behavior stop, what causes it, or why it's happening and while it's often the same keybinds that go /poof/ it can be seemingly random keybinds too.
If anyone knows a fix I'd greatly appreciate it. It's driving me nuts having to assess my keybinds before play and match everything up with my spreadsheet [made specifically for this choir]; I got sick of going into battle and a critical keybind is reset to Not Bound.