I was able to roll back mattermost to 5.34.3. And everything is back to normal.
So I now know the issue is clearly 5.35.
But a new problem has emerged.
If I go into the sytem console I can only access teams and plugins sections. Every other function is missing.
The error log has this:
{"level":"debug","ts":1620343742.3338225,"caller":"mlog/log.go:211","msg":"You do not have the appropriate permissions.","path":"/api/v4/config/environment","request_id":"c1u9pnj86iy3pm519qirrfoyfo","ip_addr":"172.17.0.1","user_id":"qsh5y3z3d7dzbkngrfpyjmzzth","method":"GET","err_where":"Permissions","http_code":403,"err_details":"userId=qsh5y3z3d7dzbkngrfpyjmzzth, permission=sysconsole_read_environment,"}
How to fix?