Thanks for reporting this. Your analysis and fix are spot on - I’ll add your fix to our code.
This actually is introduced in 4.26. In prior versions we were generating the UE4 assets to wrap FMOD studio items on the fly, which meant they were always loaded. As of 4.26 that asset generation is done only in the editor and the generated assets are serialized to be loaded at runtime so strong references are required in places like UFMODAnimNotifyPlay::Event in order to force the required asset to be loaded on demand. We already changed weak references for strong references in most instances but we’d overlooked this one!