this is not a bug, there have been changes to the file structure in 1.16.2 pre1. please refer to changelog and edit your files accordingly.
Can confirm this error in 20w28a and 20w29a, as well as with sliced_lime's example code, both tweaked and left unchanged.
I'm sorry I didn't comment sooner, I forgot about this thread. Do not use name changing scoreboards. As soon as I deleted my teams on the server everything reverted to normal.
Confirmed on my end. Entire server is booted every ~60 seconds.
I'm also having this issue with a custom dimension, no fix for me yet. I think most of us also have location based avancements?