This might be only on my end... idk, but...
Frequency: Every time attempted.
Class/Level: Arcanist, Summoner, Scholar.
Steps:
1. I've not tested this on any other character, so as far as I know, this only happens to Hyur Midlander Females. So start with this, and be a job that equips a grimoire.
2. Activate sprint, and then draw your weapon.
3. While running forwards, sheathe your weapon.
4. Watch your sword arm flip through your body and back into place!