Hello。
I want to know about this What device is JUN, as other devices have IP addresses or names, which is quite confusing.
I would say: filter for that and have a look at the log.
From my experience I would say this might be some syslog which is a bit broken.
You can try to add the field “gl2_remote_ip” in your “All Messages” widget and see, who is shipping this strange logs.
From my experience its most likely a Cisco IOS device, depending on their settings they dont follow proper syslog format. Do what @ihe described to find which one, snd then you would probably need to change settings on the device.
Cisco is well known for that. Across all their devices, firewalls, switches, routers, … 
Hahaha, do you have any suggestions about this? After all, they are all Cisco devices
for those devices create an extra input and make it as a “TCP RAW” or “UDP RAW”. You might have some glibberish start of the message, but after the header it should be like syslog