This question already has an answer here:
I've checked the migration stats pages on the sites I have access to them English Language Learners and Movies & TV and the stats don't reflect the actual migrations at all. It seems to be having trouble attributing the migrations to the sites they came from or were sent to.
Here's the ELL page:
As you can see, there are 190 migrations that apparently come out of thin air (most of them are from ELU). The system is able to correctly attribute a few from ELU and one from French. Similarly, in the away column, the two that were migrated away don't note where they were migrated to. In this case, they were both migrated to ELU.
A few months ago we noticed an odd migration error similar to this that was related to the Meta URL change. I don't think this is related because these questions aren't from Meta to Main site, they are between sites.