This is a regression from 4.24.3 (CL-11590370). SSR begins to flickers when AA is disabled when moving around the scene.
This was reported and tested in 4.25 (CL-13144385) and reproduced in Main 4.26 (CL-13408123)
Results: Screen space reflections flicker
Expected: Screen space reflections should work as per previous versions
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-93360 in the post.