Hello Kapsner13,
A violation can occur if the maximum number of macs is exceeded, which is not the case here
or
if a mac address is learned on a secured port and is moved to another secured port in the same vlan.
Is the third pc being moved from one switchport to another switchport in the same vlan?
Another question, how are you connecting these multiple devices to one port?
Does the port need to be a trunk port? Can you try an access port?
I would also do a show log | i 1/0/11
and look for any errors related to that interface.
Hope this helps,
if so, please rate.