For the Close Tab, users are not able to close this out without receiving the Warning message "Compulsory items are not filled out".

Example of the message:

Yes this setting is located on the close object - all we need to do is untick the "Restrict Incident Closure until all Required fields are entered" and this will solve the problem with the error message. Essentially the setting is indicating that the record cannot be closed until all mandatory fields across all objects are filled out. If this is accurate behaviour then leave the setting, otherwise you can remove it.

Note: There is another setting which will restrict the closure also if there are outstanding actions “Restrict close status editability until action completion”.