Sorry don’t have grid or anything so can’t really help… but I’d just look at each error in turn.
The recv error looks likes a network error , perhaps cannot connect to another process.
The no method error is sending a message to serialosc that it doesn’t understand
This is because your sending it % , this to me looks like a substitution error somewhere
What I would do is try sending a hard coded message to serialosc and checking you don’t get this message…
If no issues then it looks like an issue with connecting to other process.
In which case you need to check to see how serialosc is being started - there are subtle differences between Raspbian and arch Linux.
What I’d do initially for testing purposes is run serialosc manually