That's my main concern too, the fps variation is awful. I was chronoing on .20g bb's yes. I cleaned the barrel out earlier and it took 6 pieces of cloth to clean it, and the FPS was a little bit more consistent, but still low.
I actually have the "Specna Arms SA-H21 EDGE 2.0" and it's absolutely fantastic, but wanted to upgrade to something with full trades because I'm a sucker for authenticity. Sadly it seems I've got a lemon, because reviews I've seen all say how good the Umarex A5 is. Externally it's all I could ask for too.
I'm hoping PB will respond and allow me to send it back to them to have whatever issue(s) it has sorted out, but I put my optics etc onto the rifle so it has signs of use already, hopefully they won't refuse to touch it because of that. 🤞