in the function FinalizeVirtualTextureFeedback, the micro "USE_DBUFFER && MATERIALDECALRESPONSEMASK" returns true on mobile forward, while there is no DBUFFER on Mobile forward obviously. This takes in some unnecessary branch code, and somehow causes the vLevel incorrect on Android Snapdragon Platform.
For repro details of the original specific issue speak with Yangke Li.
But after the suggested code fix is applied you can see that DBuffer is no longer supported on mobile by using ES3.1 preview mode in editor with QAGame TM-Decals map. (Before the change the DBuffer decals did show something, but it could be incorrect, and also an assert would fire).
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-110652 in the post.