FAWE has collected quite a few upstream diffs over the years, which need to be addressed to ensure compatibility (especially with 3rd-party plugins interacting with the WE api).
This issue contains known problems:

• EngineHub/WorldEdit@6e2b0a1 (Clipboard#transform(Transform) does not exist in FAWE)
• Record-style getters are missing (affects WorldGuard support): EngineHub/WorldEdit@0df2b6a