@takeshitakenji How many unhandled items do you have in your queue_item table?
SELECT COUNT(*) FROM queue_item WHERE claimed IS NULL;

The total number of queue_item entries is interesting too (just drop the WHERE statement above).

If you activate debug logging you might see more info in your GNU social log, unless you've already done so. Occasionally I've had an issue with a queue_item being repeated indefinitely. Each time I fixed the bug, but there are of course unknown unknowns in the known unknown.