Local network already rebooted. And other services that using the same technique to acces local resources are working perfect.
So it has to be a Homey related issue.
Thanks for the replies.
It turned out to be a local issue after all.
After a while of troubleshooting I discovered that the Pihole adblocker was blocking a lot of traffic since last night. It began around the same time as the new Homey firmware was deployed.