When the Hardcore Revival mod is installed, right-clicking while crawling will cause the player to cease crawling server-side, while the client remains in the crawling state. Releasing the keybind and then pressing it again corrects the issue. I suspect this may have something to do with the way Hardcore Revival uses right-clicking to revive fallen players.

Steps to reproduce:

1. Install Personality alongside the Hardcore Revival mod.
2. Enter a world and construct a one-block-high gap that can only be entered by crawling.
3. Hold the crawl keybind, then right click (with any item, or with an empty hand). Observe that the camera position jolts upwards before sinking back down again. (It appears that the bug specifically occurs upon releasing right-click.)
4. Attempt to crawl into the one-block gap. Observe that the player rubber-bands back out due to client-server desync.

I've also reported this issue on the Hardcore Revival issues page, since I'm not sure which side this issue would best be resolved from. The corresponding issue report is here.