Lagging and layers/symbols disappears

I'm using version 21.0.5 on my new macbook pro, trying to create an animation out of an old watercolor painting I made once, but I've been having trouble playing it back since half of my layers disappeared from the stage (not from the frame panel). It was also lagging and moving really slow. I fixed that by changing a couple of things:

1. Merged my layers (about 50, to 4).

2. Checked the "match FPS".

3. Scaled down my animation to half the size.

4. Changed the publish settings: machine: level 2

5. Changed view: preview mode: fast

6. Made sure I have memory (380gb free)

This helped the playback, but whenever I export my animation, the same problems occur. Part of my animation (those that previously were individual layers, but not only one layer) still disappeares. Different parts gets scaled up and weirdly cropped for a few frames, then back to normal. Just generally laggy, and I don't understand why.