Hiya,

This used to be 2 stores (an Iceland and a Lidl), about 4 years ago the Iceland shut down and the Lidl expanded into the space. There should only be one building (which is very oddly shaped) which is now Lidl.

WRT to the multipolygon, I think that was probably the effect of me using BuildingTools to combine the shape into one without realising that's not the same thing as a single polygon. 

I think the best option is to probably trace this as a single building/polygon with just the Lidl in it, unless there's a quick and easy way to convert that into a polygon?