You may have fixed a threading problem, such as tension or bobbin threading, by changing thread. You might also have just gotten a bad spool of RA; that happens sometimes will all brands of thread.
I don't use RA cotton thread because it seems to leave more lint in my machine than other brands of thread that I use. When I sew with RA, I end up cleaning my machine about three times as often as with others. I can't even get through an entire bobbin of RA thread without my machine telling me that the bobbin area needs to be cleaned.
I wish I could use it, because the line has beautiful colors!