Version 22.214.171.124 of The Events Calendar plugin broke Toolset Forms.
When that version (or later) of The Events Calendar plugin is active, then post forms which submit posts fail to create the posts (the form reloads with a validation error because of a missing title), while with post edit forms they appear to submit correctly, but any changes to the content are not saved.
The issue doesn’t occur in versions up to 5.5.0 of The Events Calendar.
We will look into this further to see if there is anything we can do on our side to prevent the issue.
In the meantime avoid upgrading the Events Calendar beyond version 5.5.0.
As a workaround, the issue does not occur if the forms are set to submit via ajax.