I have seen a similar issue on nim devel too. I am trying to create a reproducible example for that.
I also see runnableExamples trying to get executed from sequtils.. My Nim module does import sequtils, but there are no runnableExamples in it. Also, I think this issue happens when I have \--path switches in my config.nims .. the nim doc doesn't seem to find modules that are specified via \--path or \--NimblePath. It only recognizes packages installed in the default ~/.nimble.