TexasSunshine has hit the nail on the head and probably diagnosed your problem. And, my long arm was doing the same thing today. I thought it was because I was using a thread that I had not used before. My Nolting is from the 1990's and can be a bit spiffy about the thread it wants me to use. Well...My husband came in and told me he would rethread the upper thread. I missed one spot. As soon as he did that, it has been behaving beautifully.
FYI....Almost all the time, if there are loops on the back, it is from the top thread.
Just thought about...once when mine was doing intermittent throwing of loops, the upper thread was binding and then releasing quickly. The way I found it was to glance back & forth from a practice piece to the thread path. I saw it at once. I rearranged my thread delivery and everything went fine after that.