Hello Jeroen,
Are you logged in to the Salesforce client. This is a requirement for the highest priority to kick off.
You might also want to check you have the following permissions.
Telephony > Plugin > All permission
Telephony > WebRTC Alerting Priority > Edit
Telephony > WebRTC Alerting Priority > View
If you have all of this done, my next recommended step is to open up a case with Customer Care. As it sounds like something is not triggering on the Genesys side.
Cheers,
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Cameron
Online Community Manager/Moderator
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