It is probably due to temporal antialiasing. Temporal antialiasing “averages” scene over many frames, what is super for achieving metallic shiny look but has some drawbacks, like the one you have described. Put PostprocessingVolume to the screen, make it unbound (affect while screen) and change the settings for temporal AA to MSAA (or no filtering). It is under advanced settings i think (just search for antialiasing). If you game does not have metallic surfaces, this might work better. You can probably also change the setting on per-project basis in rendering settings (don’t have access to the editor atm to check it out).
With that said, you will probably want to keep temporal AA if you have metallic surfaces. You can probably tweak some parameters though (like how the images get composited). When the scene is more full, the anomalies is less apparent in my experience. Hope this helps.