If you use the same AnimSequence in multiple SequencePlayers in Base AnimBP and replace asset of one of SequencePlayers by AssetOverride in Child AnimBP, the result will be reflected in the other SequencePlayers as well.
Probably this issue is due to the fact that under the above conditions, only 1 AnimSequenceBase is stored in the ConstantProperties of UAnimBlueprintGeneratedClass.
And you can tentatively solve this is by setting the AnimSequence property of the SequencePlayer node to Dynamic.
Expect : AssetOverride works correctly
Result : The setting in AssetOverride and the playback result in Viewport are different.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-158068 in the post.