The Play Store by default on uploading an OBB will check it against the others uploaded so if you are uploading multiple APKs built for different architectures in the same packaging session the OBB files will be identical and it is easy to get them mismatched on upload. Adding the store version as a part of the OBB file content will prevent this and make it less likely a user will mess up the store upload (you only get one chance to get it right).
Compare the main.1.[package name].obb and main.2.[package name].obb binaries. They should not be identical or Play Store will flag it on upload.
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-79037 in the post.