My dev buddy sent me a new version for a master character blueprint, including custom components.
After copying the files over existing files, HUD was displayed twice and EXP not working (related to the custom component).
Only after removing the custom component from the master character blueprint, and readding it, the custom components in child character blueprints were working, resolving the issue of double HUD and EXP not working. There was no error, whats so ever, everything seemed fine with the component, since it was attached to the master blueprint (which we use to create other characters from).
Unfortunately we cannot replicate the issue, since it has been resolved,