Only tested on a world with these specifications:

Multiplayer, I am not host, I am not OP, survival mode.

The moment I attempt to type  command in chat (typing the solidus "/"),  my device lags a great deal, usually freezing right away for a few seconds before it finally shows some of the text I typed (but not all of it (so it looks like I just typed random letters, I suppose)); it then proceeds to crash.

The host of the world does not suffer from this issue, and she also uses a Kindle Fire (not sure what gen though).

This was never a problem before 1.17.0