I know I am a bit late to this but,
Many years ago I had a machine, make unknown, that I had bought when I left home as a cheapy.
I tried using it many times and it rarely worked without a whole load of bunching under the plate and fabric. It was only after nearly throwing the thing out the window that I realised you could
not use any kind of different thread in the bobbin to what was going on the top! Same thread, different colour? Bunching! Different thread, Same colour? Bunching! I only had a couple of bobbins that came with the machine and had just been using it for the odd bits of household sewing so had never really thought about it.
To this day I would not ever, ever dream of starting a project without first ensuring there are newly wound bobbins of the same thread I am working with, let alone buy pre-wound. You need to be careful with them machines, some of them are really temperamental