Had the same problem, fitted the shower and worked for the first few times, then had intermittent problems with the button not releasing when trying to turn it off.
Took the cover off and refitted the cable and pipework plastic cover (bottom right corner) and ensured that cable supply wasn't pressing against the cover causing it to distort.
Works fine now, but I have to say it's not the best design in the world.
Russell Rees, November 2022