It looks like there is some issue with a material expression node. The error line I believe to be important is this one:
UELinkerFixups.cpp.obj : error LNK2019: unresolved external symbol “void __cdel EmptyLinkFunctionForGeneratedCodeMaterialExpressionGetSharedInput(void)”
There are three lines like this, and they make the build fail to package. Any help would be very much appreciated, I hope to start pushing this app to beta soon!