The volume drop happened on every effect, not just on one specific effect. So the volume drop happens when I select the chorus or the phaser for example.

I have recently downloaded the beta firmware upgrade. At low volumes, a volume drop wasn't noticeable. I am playing live on Friday night at volume and will report back then to see if this has cured it. 

Also I wouldn't have thought the bypass mode would have made any difference. The whole effect is attached to a Gigrig loop switcher, so is switched on all the time. I activate the effect by selecting a switch on the gigrig device. I have tried the effect in different loops to see if it was the switcher at fault. It wasn't. 

I hope the firmware download has fixed the problem. 

Since this is a "beta" firmware upgrdade, I don't quite trust it and will search on this forum to see if there has been any issues with it…

I am very grateful for your reply