This is going to be a tough one I think.
It's a nice growly flatwound that's an odd one out in a set that came with the bass. Haven't found anything to match it. I think it's an A strung in the E position ... so detuned and that may contribute to the growl ... that and it being on a fretless.
The only other distinctive thing is that there a clear gaps in the windings ... gaps on labellas are much tighter.
Pics
Any help would be appreciated as I'm starting to get obsessive about the sound of this string.
Andy