System Information
Operating system: Darwin-15.6.0-x86_64-i386-64bit 64 Bits
Graphics card: Intel(R) HD Graphics 6000 Intel Inc. 4.1 INTEL-10.14.74

Blender Version
Broken: version: 2.83.0, branch: master, commit date: 2020-06-03 14:38, hash: rB211b6c29f771
Worked: (newest version of Blender that worked as expected)

I merged two layers in 2D grease pencil and shortly after my computer slowed down and now every keyframe stays on screen and stacks/overlaps on top of one another rather than moving frame by frame.

The second layer only had a few frames (I accidentally worked on a new layer instead of the line layer I had been working on), so it's not like the frames from the two layers are overlapping. When I originally animated I added onto and erased parts of the previous keyframe, but now it seems like I only added and everything is on screen at once. For example, I animated a character lip syncing (every time I made a new keyframe I just erased the mouth and redrew it) and now the mouth is a large combination of every mouth I drew throughout the animation. You can also see how every breakdown is displayed onscreen in the interpolation sequence I used on the right. This was my first time using blender so I thought it was a simple mistake, but I couldn't find a solution anywhere so it's probably a bug.

I'm sorry, I'm really not sure how to recreate this since I'm not sure how it happened in this first place. All I know is that all my frames are staying on screen and it may be due to the merging of two non-overlapping layers in grease pencil.