Good news!
The slow down Lag/responsiveness with OSC in fixed learn mode also happens when the script is not even running (closed with the x button).
This means there is something that every so often screws up OSC control.
To be honest it might be my router so I need to try an adhoc connection to see if that solves it.
Least that part (for me at least) means that it's not the mapper script.
Not being able to delete learnt osc though is still there