Getting the same error. From what I’ve gathered there could be some kind of corrupted variable in a blueprint somewhere and the only way to know which one is by going script to script deleting and recreating every var until it builds. Sounds incredibly tedious, I really hope we get a better answer soon 
Edit: I made a hotfix that ‘fixes’ it and doesn’t require me to go through all my files. Definitely not an optimal solution, and will only work if you work off of the engine source code.
In Engine\Source\Runtime\CoreUObject\Private\UObject\SoftObjectPath.cpp on line 74 there’s a check to see if an object path is set to ‘None’ in which case it calls Reset(). I just added a check to see if it is either ‘None’ or ‘NoneNone’ then do the same logic.
My guess is that there’s some functionality that sets an object path to ‘None’ (either to mark it as soft deleted or if it doesn’t need its path for some reason or some other reason) and that functionality is a bit busted and just appended ‘None’ to an object path that had already been marked as ‘None’. Then the error handling isn’t equipped to deal with the cases where there is more than one None in the path.
Here’s my hotfix you could copy into SoftObjectPath.cpp starting with line 72 and rebuild the engine, this worked for me until a faster real fix comes out:
void FSoftObjectPath::SetPath(FWideStringView Path)
{
if (Path.IsEmpty() || Path.Equals(TEXT("None"), ESearchCase::CaseSensitive) || Path.Equals(TEXT("NoneNone"), ESearchCase::CaseSensitive))
{
// Empty path, just empty the pathname.
Reset();
}