I had one go wonky on me. I had done all the work and had shot it into the .2's.....but just haaaad to index the barrel another. 001" to sleep well.
I did so and the rifle shot poorly. I chased down everything possible right down to the chamber runout. I put it back together and the rifle tipped over and made a funny noise. I whacked it with a rawhide mallet and I found that one of my Warne rings was cracked. I couldn't see it but I could hear it. When I tore the scope down it was obvious.
Now I smack them all with a rawhide and listen.
Glad you found your culprit and it was cheap.