Custom Integration sync is stuck: Cannot cancel sync nor Disable it

I paused my integration service during debugging, while Fibery was doing a sync.

Usually Fibery just reports that the socket was closed, and cancels the sync.

But this time Fibery did not detect the closed socket, and now it appears stuck –
I can neither cancel the sync, nor Disable the Integration:

Eventually it stopped trying (“Sync failed”) and then I was able to Disable the integration.