Players no longer recover their inventory when leaving the jail! I don't think I changed anything that could have caused this except the regular updates ...
An idea ?

If you're using the Restore Upon Death plugin it can interfere with the Jail plugin.  I corrected the issue by having RUD reference Jail and check to see if the player who died was a prisoner and not allow RUD to handle the player inventory so Jail could do what it should.

Merged post

I had to do some more updates actually to get the Jail plugin and the Restore Upon Death plugin to work together properly.  Both plugins were created by the same author, but it doesn't seem like he's maintaining them anymore.  He also wrotethe Bounty plugin which I was also updating to allow sending killed bounties to Jail.