Laggy screen when underground in spectator mode

Please force a crash report (F3 + C for 10 seconds, stored at minecraft/crash-reports/crash-<DATE>-client.txt). I was unable to reproduce this on my existing world.

I have this problem, too. It occurs if I turn on chunk border rendering but also randomly happens in just normal spectator mode. I can eliminate the lag by going above ground or into a cave.