Hi @aleksandarsh_4585 ,
I wanted to put the final solution in this thread for what solved the error. It looks like the issue was around which extensions were installed. After upgrading to 6.1, you needed to enable the legacy features in Administration > Advanced Settings and install the Legacy extensions in Administration > Extensions. We also had to uninstall and extensions that had errors loading including Amazon, Jira, and Jenkins and only leave the legacy versions installed.
Thanks,
Rich