I get "High Rate of STP Topology Changes" on all of my Meraki Core switchports that are connected to other non-Meraki switches. Should I be concerned and what would be my next steps in troubleshooting this?
Agreed, I'd confirm all of the physical connectivity and do some quick packet captures or work with Support to find the source(s) of the TCN BPDUs and start from there, possibly even temporarily admin-downing certain redundant/blocking links to isolate the issue.
Have you configured the root priority for the switch that should be the core of your network?
Next the other switches, what are they? If they are Cisco Enterprise switches I would configure them to use mst "spanning-tree mode mst".
If they are dumb layer 2 switches it is possible they don't even run spanning tree.
Look for links between edge/leaf switches that should be there. You ideally want a loop free design where the downstream switches only connect to the core switch and no other switches.