Shelly Event URL not working anymore

I created a rule to send notifications when a Shelly 1 is switched. This worked several months until I tested a dev-build of the Shelly binding.
The URLs are correctly registered in the device, but if I copy an URL (e.g. http://192.168.178.xx:1234/shelly/event/shelly1-123abc/relay/0?type=btn_on) and test it via browser, I get a HTTP 404 response. The log doesn’t change.

I switched back to the release-build, cleared the “openhab/userdata/logs” and “openhab/userdata/cache” folders and updated openhab to Version 3.4.4. Nothing worked. What else can I try?