EDIT 2: False alarm. Turned out to be a faulty loot_table (just a single comma after the last entry in the rare drops made it crash every time it rolled for a rare drop).

Old message: When firing arrows (bow is in offhand) the game sometimes crashes. The error report seems to indicate that getting a null pointer exception when checking for vehicle is the problem. Possibly the check for all basic stats taking longer than the arrow exists (maybe 1 to 1.5 seconds between arrow creation and it hitting a zombie and thus ceasing to exist). This is the relevant line:

Entity's Vehicle: ~_ERROR~ NullPointerException: null

EDIT: this happened 3 times in 30 minutes before I reported it. Just normal everyday arrowplay. Although that mouse button is glitchy and sometimes thinks I pressed it 2 or 3 times. Could it be a canceled arrow from pressing the button for too little time?