Ok, tonight I gave it another try, with success.
In the file “org.apache.felix.eventadmin.impl.EventAdmin.cfg” (stored in userdata\openhab2\etc) I added a new parameter:
org.apache.felix.eventadmin.Timeout=0
If you don’t have that parameter (like I did), it defaults to 5000ms (source). If you set it to “0” there is no timeout. In my case, the OH core got “blacklisted” because: “If an event handler takes longer than the configured timeout to process an event, it is blacklisted. Once a handler is in a blacklist, it doesn’t get sent any events anymore.”
After setting this parameter, I upgraded back to #1084. On first boot, it took very long for OH to start. After 10 minutes, I initiated a restart. After that, OH started pretty quickly without any errors.
So now I have a working #1084 build. 
Not sure if setting that parameter is “best practice”. So I wanted to check: does one of you guys have a specific value set for this parameter?