Trying to export a build in UE5.3 but fails with an unknown error. As I scroll up the output log the only errors I have are these. Not sure what the fix can be. 
UE5.3 Windows Build Error
Apologies, it looks like Epic changed the compiler flags again with 5.3 for Windows. I've added an issue on our tracker:
EsotericSoftware/spine-runtimes2633
Mario I was able to package a build successfully. These errors don't really effect the game. Turns out I needed to delete my saved folder inside my ue5 project in order to build.
OK, that would explain why I couldn't reproduce it with our example project. Thanks for reporting back!