Every now and then one of our users Nokia E7 (with latest firmware
updates) stops syncing. Re-initialize user from management solves the
issue but after this users mails are starting to move from "sent items"
to trash box on Groupwise client side, about 30-200 mails during each
mobile sync.

Some other users use E7 just nicely.

Mobility (v1.2.0.2572)

Any ideas what could be used to troubleshoot this?