I have seen a few complaints about structs in arrays since blueprint-created structs were released. Probably need a dev to chime in.
If you are afraid of this problem and how long it might take to fix if it is a bug, then you can still work around the issue.
You can keep each buff’s information stored across a series of arrays. Value, Duration, AP Cost, etc arrays. Then each of your buffs has an index that is shared across all of those arrays. If your character gets buff # 5, then you search that index across all the arrays to pull the properties.
Anyway that is one way to do it, at least until your struct issue is resolved.