I have been having an issue on my server where the clock/time doesn't do the full cycle, it goes from 20:00 to 10:00, without going to 00:00. Day time lasts for a few minutes and then its night again. Before 20:00 the sun is rising, and after 20:00 when it skips to 10:00 it begins to set instantly. The sun never reaches its maximum height, so daylight is almost non-existant. I have tested the modpack on a single player world and time works fine, the full 00:00 to 20:00, yet the server fails to work properly.
There are no errors or outputs on the server, even setting the time through commands yields the same result, after 20:00 skipping to 10:00.
The server runs at a full 20TPS most of the time, dropping to 15TPS at the lowest, I am using forge-1.12.2-220.127.116.1138