Sorry to hear you are having issues. I am unable to reproduce this. When I toggle force mono I can see/hear the level decrease, then if I power off the H90 the signal is not summed to mono anymore and the level increases, then when I power the H90 back on the signal is summed to mono and goes back down to the previous reduced level.
Can you try this with two THRU algorithms and let me know if you experience the same issue? Are you able to hear if the stereo input is summed to mono when this happens?
It would be best if you can email support@eventideaudio.com with a video that demonstrates this issue. If you can show the output being monitored in a DAW or some software with audio level meters that shows the difference in volume, that would be helpful,
