I had something similiar happen to me. I'm in the process of converting to 15 pounds from 16 pounds. With the 15s, I went back to an approach I hadn't used in 10 years, and I wound up averaging 230 with it over the summer. This fall however, everything collapsed and I started out with 171. Starting in week 3, I went back to the 16s using the approach that has worked for the last decade and I started coming back up. At the same time I was working through timing issues with the other approach. I used it again this past Monday and had a 200 and 198 for the first 2 games. After I made one last adjustment, my last game was 263.
Sometimes it just happens. Either you just have an off-night or something else started going wrong. I went from throwing 660-710 per week down to 530. I just went back to what I knew would work, while bowling through the timing problems on the side. I'm not sure if I'm out of it yet, but I'm much closer than I was 2 months ago. It'll come back to you. If it just an off-night (which is probably what happened) you'll recover quickly. Otherwise, you might have to try to determine if something is wrong like I'm having to do.
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On league night, a realm of untold destruction and horror is formed. Innocent pins are unsuspectingly pulled into this terrifying realm. Their lives are changed forever by the terror that is unleashed upon them for the next 36 frames. They stand in fear as they await their fate when they enter...The Danger Zone. (Only those damn 10-pins have lived to tell the gruesome tale.)