In our case, a symptom that our Cisco Swich has reached the limit of its traffic management capacity at moment in time is the "LOOPGUAR_BLOCK" and "LOOPGUAR_BLOCK" alerts
We can reproduce this problem when we move/copy big information amount. Example move Virtual Machines, Backup, etc.
A few of Literature:
"LoopGuard prevents alternateor root port from becoming designated in absence of BPDUs."
"Protects alternate (blocked) or root (forwarding) ports from moving to forwarding upon no receipt of BPDU’s."
"If a Port Receive state machine receives an inferior RST BPDU from a Port that believes itself to be a Designated Port AND is Learning or Forwarding it will set disputed, causing this state machine to transition a Designated Port to Discarding"