Adding on to output of "show stpd ". Check the information in the field "Topology Change initiated locally on Port". This gives an idea as to where to start looking for in the switch.
Also, the logs can give you an idea if there had been any port flap seen in STP configured port that might have also caused the TCN to be generated by the switch.
Just a word of information, if the STP is configured for auto-bind ports, please configure STP edge on the host connecting ports to aviod the unnecessary generation of TCN.