Confirmed appointments still available

it used to work fine. Now, after I change the status to Confirmed, every slot is always available.
I've disabled all other plugins. No jquery errors.

Plus, I am having this message after that last update:
"There seems to be something wrong with the WP Heartbeat API state. The "Pending Appointments count notification" add-on might not work properly because of this."

I can provide url privately.

Thank you