I’ve been told (so this may or may not be true) that it is the fumes that cause the polycarb to become brittle. I know from experience that any loctite near polycarb will eventually cause it to crack, so there is some reaction.
TLDR, don’t use loctite on or near polycarb.
There is a “plastic safe” loctite that apparently works (Loctite 425), but it can cause a minor strength decrease.
I would read through Loctite testing (was: 1678 Robot Reveal 2022) - #8 by Patrick3357 for more info.
What i would recommend is either trying to only use nylocks, or if you can’t, no loctite or something like this