Some information

Operating system: Windows
Java version: Have multiple installed for dev work; client java_version tag says 1.8.0_51
Minecraft version: 1.12.2-Impact_4.8.3 (hacked client with Baritone integration)
Baritone version: Unknown, as not installed directly--Whatever above client version uses, which was not easily visible on their Github
Additional mods: Impact anti-desync, possible cause

Occasionally when there is 5-10 TPS on a server, a bot will be pillaring up to the Nether ceiling and will get stuck inside its most recent block, being pushed to the edge and rubberbanding to its center. The effect disappears upon mining the block manually and is not present upon restart of the pathing but during its duration, the bot endlessly recalculates its prior path. I've only seen it happen on the second-to-last block placed (i.e. bot pillars a bunch, breaks a hole in the ceiling, gets stuck in next block placed under feet) but this could be random chance.

This is potentially a result of Impact's anti-desync setting, which prevents mined and placed blocks from reappearing/disappearing, presumably by not breaking the block client-side until server confirmation is somehow obtained. The bot seems to perform worse without it, and I can't justify sabotaging server TPS to replicate without this hack enabled.