I'm posting this here because this bug/lag only happened to me with this mod.
The game experience perfomance issues during most of the engagements (especially when there is a lot of shooting), I'm aware that BtA is a "heavyweight" mod but I noticed that when looking at the sides, my rear o using the freelook camera (in all this three cases the HUD disappear) the game become fluid again (back to 60 PFS) most of the time.
I haven't been able to reproduce this perfomance issues with any other mod. I also tried launching the game without v-sync or some other HUD elements deactivited but it didn't fix the issue.
It's the first time I encounter such lagging on FSO that's why I'm posting it.
In case this could help: https://fsnebula.org/log/5e495582cb0d3321b2c98611
Thank you for your help!