[Dridzt]

The d/c issue is probably WoW hitting the 5.1.x script execution time limit if it happens in combat.

The issue is exacerbated by the fact that not all methods of checking for combat status are reliable during a reconnect (or reload) even if the addon was actually trying to detect combat and defer costly operations.
In particular events (like PLAYER_REGEN_DISABLED) and InCombatLockdown() are not trustworthy in that situation.
UnitAffectingCombat(unit) seems to work better in that situation, or you can code in a way that you always assume In Combat status until such time as you can trust the client to return good information whence you perform the actual test.

If the client hits the script execution time limit (whether you have lua errors enabled to see the "script ran too long" error or not) it is typical that your FPS will crash and probably not recover until a /reload out of combat.