So I think I've mentioned on here before that the only complaint I really had regarding the jvm was the fx loop. Just wasn't my favorite and it seemed to have some weird quirks.
Well the amp actually has 2 separate FX loops. The "main" loop that is footswitchable is called "series/paralell loop" (wtf does that even mean which one is it? lol) with a mix knob and +4/-12db option switch. I've struggled the entire time I've had it to get my FX sounding as I like and still balancing the mix knob without creating too much tone suck (which it does quite a lot) and again it just all behaves kind of weird.
Now the other loop is called "Power amp insert/series loop" everything I read online and the implication from the manual indicated that this was not designed for pedalboard FX and that it is a line level passive series loop. That "wisdom" plus the fact that series loop has a negative connotation right off the bat based on my experiences with my old rectoverb etc. (edit: I smoke too much pot and I had series and Paralell mixed up

Well I randomly decided to try it today, and low and be hold it is SO MUCH BETTER. my delays and trippy reverb sound great and like they're supposed toand it's not all weird with my looper pedal. Best part? waaay less tone suck than the other loop. I'm never using that thing again

Moral of the story, always experiemnt, and if you have a JVM and find the "normal" loop to be lackluster, give the other one ago