Immediately after logging in I get client lag that brings me to 3 FPS for 10-15 seconds. Disabling BagBrother (which disables Bagnon) makes the lag no longer occur.

I deleted the cached characters I had but it doesn't seem to help

Same issue, immediately after update 10.0.7 for WoW-10.0.2 except log in screen sticks with full blue bar and WoW goes flat out unresponsive for several minutes.
Disabled Bagnon, no issues. Deleted Bagnon, no issues.
Was really looking forward to having Bagnon back again.

same also during the mega lag im unable to even alt tab back into the game before the lag has stopped.

Similar issue is discussed here.