Fixing lace seems to be a puzzle. Twice so far my yo's have shifted one st to the left of where they should be, thereby wrecking the nice diagonals. Another time a half row insinuated itself into one side, also wrecking the diagonals and introducing some lumpiness.
I never did figure out how these problems happened. In the first case I managed to rip back to the row before the shift happened, but it took about 5 tries and some fudging to get the next rows aligned properly. Luckily a friend told me how to do a lifeline easily so the next 2 issues were corrected more easily.
Fortunately probably due to all these rewinds I can now recognize where those sl sts and psso's and yo's are supposed to go and that makes it easier to spot where things are going wrong so they can be fixed with minimal disruption.