I have been having this issue as well with a zombie and skeleton farm. Both are being used in a Bedrock Realm that happen to be within ticking areas. After reading this I believe, but cannot be 100% sure, that the minecart hoppers have only disappeared after a crash that results in a rollback of 15-30 minutes (twice now). They don't get stuck or anything, they literally disappear. While not the worst thing ever, it is a bit of a pain of a bug.
John Crowley III
I have been having this issue as well with a zombie and skeleton farm. Both are being used in a Bedrock Realm that happen to be within ticking areas. After reading this I believe, but cannot be 100% sure, that the minecart hoppers have only disappeared after a crash that results in a rollback of 15-30 minutes (twice now). They don't get stuck or anything, they literally disappear. While not the worst thing ever, it is a bit of a pain of a bug.