I was having a very similar problem with my LA. It had been sewing fine and then started giving me problems, and they kept getting worse - it was the same, I'd get a bit snag of top thread on the bottom and half the time the thread would break.
I was thinking the machine was going to need to go in for service, and while cleaning I noticed just a tiny bit of thread that was behind the hook assembly. I started digging around (I have dental tools to get into tiny spots) and I ended up pulling a wad of thread/lint out from behind the hook assembly. I was cleaning the area with a brush every bobbing change but I guess I just wasn't getting back there well enough. It appears the lint build up was pushing the bobbin case out just ever so slightly (it still clipped in place) and that was causing the top thread to occasionally hang up on the bobbin case. Once I cleaned that area all out, the machine sewed fine and I've not had the problem since.
I now have a small vacuum that I use to help clean the shuttle area out - that seems to be working quite well to get the lint out.