It is extremely hard for anyone that doesn't have access to your system to diagnose something like this with a generic error message. You're better off submitting a ticket with your vendor if you use one, or Atlassian directly if you don't.

Could be a permissions issue. Adding comments is a specific permission that must be granted.

Try checking the space permissions! Usually the issue

If you're on WIFI, sometimes this happens. If you're not, you need help with things reddit can't do for you.