Just to make sure, that I understand this right:
Its a source from a private 192.168.254.0 that has/had an connecntion with the broadcast IP of the IpFire with a downstream of 32byte?
yes, you understand this right. Although there technically isn’t really a connection because it is unreplied and any replies will go directly to that host unseen from the firewall.
The port numbers don’t look familiar to me. But probably something announcing itself to the network. Like a printer? Some media sharing service? They should use multicasts instead, but the simpler the software/device the more likely they simply flood the network with this.