I'm getting the error - [Expression.Error] The field 'BUSINESS' of the record wasn't found. The preview is loading fine, yet when I filter this column on specific step to check for errors - it says so: 
The field is calculated in the previous queries once and it doesn't give any errors. On the 1st step - when I merge, it also doesn't show error. It happens only after I expand merged query fields (the 'BUSINESS' doesn't get merged, it's already in there). I'm ready to smash my head, because I can't see how merging can affect a field which is not being used in it at all, moreover it doesn't have any issues even before.
let
Source = Table.NestedJoin(GRID_DATA, {"KeyMatch"}, ComPolicy, {"KeyMatch"}, "ComPolicy", JoinKind.LeftOuter),
#"Expanded ComPolicy" = Table.ExpandTableColumn(Source, "ComPolicy", {"Region", "Chain code", "REGION2", "Vendor Name", "Vendor Number", "PROMOTOOL_TYPE"}, {"ComPolicy.Region", "ComPolicy.Chain code", "ComPolicy.REGION2", "ComPolicy.Vendor Name", "ComPolicy.Vendor Number", "ComPolicy.PROMOTOOL_TYPE"}),
Yet i'm also concerned why does it look for 'BUSINESS' in upper-case when I've never used it in any query in upper case. It might be the issue, I don't see the roots though.
