Well, since i've been ran 3.8.2 i have the same MySQL (5.5.33), so I'll try to use the older mysql.jar
Update: I've changed the mysql.jar from 5.1.30 (that cames with 3.9.3) for the one of my old 3.8.2 instalation (5.0.8). Let's see if it works...
Update 2: Two days running without any failure for while. I'll wait until friday to confirm if the problem was solved.