I was making an animation when i hit my 100th frame, then the onion skin disappeared. I rendered the frames to a folder and imported them, but the onion skin still wouldn't work. I tested a blank animation and it worked, so it was just my imported frames. Is there some sort of limit on the number of frames where the onion skin will not work for the entire animation once the 100th frame was hit. Any help would be appreciated.

Which version of krita and which operating system are you using?

I've just made a small animation with groups of simple painted keyframes spread from frame-0 to frame-150 and the onion skins work ok throughout.
On an existing 870 frame animation, the onion skins also work ok.

Do you have a single animated layer with content painted/drawn on a transparent background?
On the new animation where they work, do they still work if you import those frames into a new layer and then turn off the visibility of the new layer?

I'm using Krita 4.4.1 and I'm on windows 10. I'm not sure how to turn off visibility? Would you be able to explain it to me?

No i do not have a transparent background but it is all on the same animated layer.

The latest formal relese is version 4.4.2 and that will be superceded by 4.4.3 in the near future so it would be a good idea to update when that happens, or go to 4.4.2 now if you like.

By 'visibility', I meant the eye icon/button at the side of each layer in the Layers docker and Timeline docker.

When I said, "a single animated layer with content painted/drawn on a transparent background", I meant that the animated content has been painted on an initially transparent paint layer.
Any 'background' you have, such as a plain white background or a woodland scene or whatever, should be done on a non-animated layer underneath the animated layer.

The onion skins work with the presence of paint on a layer, so if each frame has fully painted content then there is no painted difference between frames, so no onion skins.
That may explain your situation but it doesn't explain why the onion skins stopped working only after you did 100 frames or whatever number.
Can you look at your animation structure and content and consider if you have solid painted content (paint everywhere) that is causing the problem?