building on a Nazgul Evoque right now and two of my motor screws have backed out twice during test flights already. im using the screws that came with the motors which are like M3x5 or something and i put a tiny bit of blue loctite on them but they keep coming loose anyway. the weird thing is its always the same two screws on the same motor so maybe that motor mount hole is stripped slightly? hard to tell by looking at it

also running into a weird thing where my FC is reading one motor hotter than the others after just a hover session, not sure if these two things are related or if im just having a bad week with this build

if its the same two screws every time the hole is probably stripped or close to it. blue loctite should hold on a good thread. you can try slightly longer screws if theres clearance inside the motor, sometimes an extra half mm of thread engagement makes a big difference. otherwise helicoil or just accept the arm is cooked and swap it, frames usually come with spare arms or at least sell them cheap.

the hot motor thing id look at first honestly, a loose motor can vibrate more and generate more heat and also a motor thats not sitting flat on the mount because of loose screws is gonna have worse heat transfer. fix the mechanical issue first then see if the temp reading normalizes.

i had nearly this exact problem and it turned out i was just not letting the loctite cure long enough before flying. like you need to actually wait, not just "ok its been 20 minutes lets go". threadlocker needs several hours minimum to really set properly on small fasteners in my experience. also some of the screws that ship with motors are just garbage soft metal and they strip easier than they should, replacing with decent stainless M3s from a proper hardware kit made a noticeable difference for me. AliExpress screw assortment kits are worth every penny for this stuff