There are many causes to trigger RRC connection re-establishment by UE. Some of the causes I have listed down.
1. Due to integrity check failure at lower layers of UE stack.
2. Due to RRC connection reconfiguration failure.
3. Mobility from E-UTRA failure.
4. Intra LTE handover failure.
5. Radio link failure.
One more interesting thing is that while executing handover. If handover gets failed then RRC connection re-establishment request can come to either side(source eNodeB or target eNodeB).
Hope this brief answer will help out.
