The Alpha Mask on a Canvas Render Target 2D no longer appears when rendering with ES3.1. This is a regression from 4.24.3 (CL-11590370).
This was reported and tested in 4.25 Preview 7 (CL-12759524) and reproduced in Main 4.26 (CL-12945139)
Results: There is nothing on the CanvasRenderTarget2D. Alpha Mask does not exist
Expected: To get Alpha Mask in Canvas Render Target 2D
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-92424 in the post.