First a general note to all: I suggest new issues should be posted in a new thread. I believe it is more efficient to post new issues separately instead of tagging it to another issue that may or may not be relevant. Sometimes even though the 2 topics are related to the same module/import/line item .... etc, the issues in each are different. I believe this way when a community member is searching for an answer to his/her question they can easily find it.
Now to the main issue:
From the screenshots you provided, it looks like the locations are not mapped. That's the reason why Anaplan doesn't know where to place the data for Beginning Inventory since we need both a location and SKU.
So your focus should be on why the locations are not mapped? It seems that the Location - and hence the list subset - may not be populated. So start from that list.
This is the same answer given in your other post here
Einas "Give a Man a Fish, and You Feed Him for a Day. Teach a Man To Fish, and You Feed Him for a Lifetime"