If it is truly idle in a transaction, maybe it has locks that are holding
up other transactions?
Locks are usually held until commit time, except advisory locks iirc but
those have to be explicitly checked, so if you don't know if you are using
them you probably aren't.
Long-running transactions are generally a problem particularly when you
have idle blocks of space between them. Try shortening your transactions
and see if that helps.
Best Wishes,
Chris Travers