Created a world in 1.6, started building, after about 15-20 hours I noticed a brief moment where I got very low FPS. I have noticed this with F3 open, it does not go below 80 FPS. This FPS lag is very noticeable, as when I turn it will sometimes flicker across my screen. It does not appear to be a timed occurrence. I also have game day cycle off with the sun at noon, don't know if this contributes to the problem.
Something that I've noticed as well is that my FPS is fluctuating from 100-300 while I've been playing.
I'm including a manually triggered crash report as well in case it helps.
Also, I looked over a lot of bug reports to see if this was not just me, I did not find anything.