Buffing LSP via PC requires a very thin application. Applying a lot of pressure to the PC doesn't seem to work well for this so you can't try to force things the way you can when doing this via Cyclo.
Not that I know from Mother's, but I can't help but wonder if it was applied too thickly.
With products like Collinite 476S, if I get the application properly thin, I can let it set up indefinitely (as in, longer than overnight) and it still buffs off easily.
If/when I do have problems buffing something off, I'll sometimes reapply the same stuff over top of the tenacious application. It's the "like-dissolves-like" solvent action thing. Doesn't seem to work with Collinite, but it does work with a lot of other products.