I ran into the same problem: VS2017, Qt 5.12.6, Windows 10, Release, static inline const QString member. interestingly, using QStringLiteral around the initializer makes the problem go away, so it seems to have something to do with memory allocation.

@koahnig said:

Thanks for your patience and continued support. I have found the problem.

That's great. I'm glad I was able to contribute. :)

Unfortunately implementation files slipped into the compilation of the application.

Ah, sneaky .cpps :)

The warning text is misleading though, but it was actually showing the cause, duplicated declarations or better duplicated implementations.

Sadly that's always the case with the linker. A linker is dumb as a shoe, it doesn't have any context or semantics to the code, it just reorders symbols and puts addresses, that's why linker error are so cryptic. :)

I myself get into a hateful depression when I get the notorious "undefined vtable for ..." :D

In any case, I'm glad it worked out.
Cheers!