Time glitch, sun keeps moving back and forth

Greetings!

When I opened up my singleplayer Minecraft world, I immediately noticed things were weird. It kept flickering between daytime and nighttime, changing about every second or so.

I opened up F3 and I saw that it was switching between "Day 125" and "Day 29" (I'd be more lead to believe it was Day 125 in my world than 29).

Please see this recording I made: https://youtu.be/wyIJpjk19dg

I tried the command "/time set 0" to see if it would fix it, and it then started switching between "Day 125" and "Day 0" instead. Eventually, closing and restarting Minecraft fixed the issue.

I have no mods installed, and have not used the "time set" command before in this world as far as I can remember; I've only slept in beds. The graphics card that Minecraft is apparently using is my Intel HD Graphics 5500 (despite having an Nvidia GPU, but whatever).