Have you tried high velocities? I think portamento engages at low vel.Bought it, love it. There's issues here and there, I wouldn't buy it expecting it to be a go-to. For me it'll be a specialized tool for slower expressive writing. Like adagios.
BTW, there's a lot of portamento in this. I'm not 100% sure, but I suspect there might be some intervals where the only connected note you can get has a portamento.