Holy moley, we have a prime suspect!
The best advice I can give is for you to do Parnell knots for everything, get a starting clamp if you don't already have one, and add 5 lbs when you tension your last strings.
(If you don't already do all of these things.)
In case you're interested, there are some very good youtube videos for all of these.
3 x Head MGPMs: Pacific Classic Gut 1.25 x MSV Co-Focus 1.18
3 x Head i.PMs: OGSM 1.22 x CoF 1.18, Energetic 1.20 x CoF & PPA 1.25 x CoF