Ah, sorry, I forgot to mention as well that this was in NW.js.
I investigated further and found this: https://github.com/nwjs/nw.js/issues/6336#issuecomment-352252411 I've been on a version a few versions back, avoiding to update in case it breaks a big project of mine. Testing v0.29.0 it seems the fix has been implemented, however, everything runs at 30 fps now (was hitting 144 fps without issues before) so I'll have to do some more testing, restart my computer and maybe try v0.28.0 too. I'll update with further findings.
EDIT:
So v0.28.0 seems to be the best solution for now if you don't wanna fiddle too much. Mouse lock works and the performance is good.
I found the reason for the poor performance with v0.29.0 (Ashley and NW.js devs are aware as you can see): https://github.com/nwjs/nw.js/issues/6498
Hopefully an updated version will be available soon that doesn't require manual handling of those command line arguments.
Thanks and good to know about the issues.