For years I have run into this bug over and over in many engine versions
And it’s still there, indeed. I’ll have you know it can manifest without enumerators, you can have it happen by merely exposing / updating struct variable, too 
. First time I run into this issue was around 2016/2017 (?) when structs declared in BPs were ridiculously prone to corruption. Since then I’ve been leaving slightly more detailed steps very much like yours dotted around the Anwer Hub and then the Forums. I reported it a bunch of times, too. Problem is, providing 100% repro steps cannot be done, can it?