You can also use existing save, but need to edit the Vehicles.XML file, just replace STORE_CONFIG to NONE. If you not using courseplay then new version is not really needed.
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There is no "STORE_CONFIG" in the vehicles.xml in either version of the map and i checked all other XML for the same thing and there is not any sign of it.
We updated to the new version hoping it would fix our issue as even with the old map version we had this issue but it did not fix it. All of us get to 100% and it then says "compiling shaders"