It's caused by Lemmy-UI's websockets client. It does weird stuff like this when the site is under heavy load (we broke Lemmy!)
It's being removed in Lemmy 0.18 and being replaced with a more stable http client. No word on when that will release, but it looks like progress is being made fast.
Sources:
https://github.com/LemmyNet/lemmy/issues/3008#issuecomment-1588120660
https://github.com/LemmyNet/lemmy-ui/commit/2b1af707c3df6126b3e6890106c03c60ad49b1be