We had one user report that their keyboard on a MAC did not work when connecting to Citrix, mouse worked fine and the keyboard worked fine locally.
Testing from other devices with the same Citrix Receiver version were getting the same non-working keyboard issue. Command-tab returns keyboard to a working state.
OS X 10.9.5 introduced a change impacting keyboard operation. When it occurs you can switch to another app and back and the keyboard will strangely work again.
The solution was to upgrade to Receiver for Mac 11.9
We also confirmed private fix 126.96.36.199815 also fixes the Keyboard issue for our users.