Okay - I worked this out. The intervalometer was running under Timelapse, which prevented me doing anything in Holygrail, going to Timelapse and stopping it gave control back. I didn't work this out from the error messages which just said "Intervalometer is running" which I assumed was the HG one no...

Canon 90d, Moto G8 Android phone, Android version 11, latest app version, latest firmware. Trying to test Holy grail. App won't let me start an HG sequence as it states the intervalometer is already running but I cannot start or stop it. Start/stop icon is the play/pause one. It doesn't respond. I c...