I'm not sure.
I've gotten round this issue by having a clean boost pedal wishing the FX loop either before or after the pedals.
I've had issues with:
EHX Enigma
Cog T16
And in both case a volume pedal before / agree has helped.
Poultone do a clean boost in a tiny enclosure
Southampton Devices do a dual boost and fx buffer in a tiny enclosure.
I have a COG clean boost too.
All excellent.