I have same problem too like this .
Video lagging after recording . Was using stock camera .
I had the exact same problem with last miui (Nougat)
Solved after clean cache and dalvic in TWRP.
I just want to say a BIG THANK YOU to all developers and all people that helps so a great alternative rom like this one (and many more) be present and 100% bug free for this great phone.
The MOST COMPLETE and bug-free rom I ever used!!!
Everything works as it should be better than any JB stock firmware Nicolas you just upgrade my P
to a higher level.
Thanks for your effords.
Keep going patrioti!!!