Going through the journal, there seems to be nothing logged before the restarts of NetworkManager, the links stay’s up.
This seems to indicate that the machine with hw adres 00:01:5c:78:42:46 does not respond properly.
For reference on my system ip -r monitor goes through a STALE - > PROBE - > REACHABLE cycle for hosts. iirc this is normal behavior, the ethernet protocol keeps a list on what is connected and refreshes the list periodically.
ip neigh will show the adress of the machine, I guess the gateway 107.11.224.1 in the previous post
Does pinging the gateway or something a bit further away (google.com?) show any drops or high latency in traffic when the network degrades?
Idea:
Using something like portmaster-stub could give some insight into the various applications and traffic they generate. Manjaro has this application in the repository: Portmaster and SPN by Safing.io