Keyboard Shortcut (Flip Horizontal) not Working in Lightroom Classic 12.1

I use the latest version of Lightroom Classic (v12.1) in English with a standard US keyboard and have just started using an Elgato Stream Deck Plus with Sideshowfx profiles and a Xencelabs tablet to improve my workflow.

Working in the Develop module, when I select Flip Vertical it works correctly. However, when I select Flip Horizontal, nothing happens other than the Photo menu opening. I checked the Stream Deck profiles and they are set up correctly with the correct sequence of keyboard shortcuts, Alt+P followed by a short delay and then H, and so I decided to try and manually input the keyboard shortcuts.

Selecting Alt+P opens the Photo menu and places the highlight on the first item in the menu (Add to Quick Collection). However, when I subsequently select H, the highlight simply moves down one line. Selecting H a second time then moves the highlight to the Flip Horizontal option, but still nothing happens until I subsequently select Enter, at which point my image is flipped. If I amend my Stream Deck profile with the extra key strokes, the Flip Horizontal works, but that is clearly not the way it is supposed to operate.

Do I have a bug in my install or is the keyboard shortcut flawed? I would be grateful for any assistance.

Many Thanks

Ned