Issue is primarily with map design, there are a ton of pixel ledges around the map especially where there are pillars, windows, and the bridges around the middle of the map. I really hope the map gets cleaned up of all these random spots, but probably much later once the map design gets fully fleshed out and stable.
They could also fix this issue by giving Abrams a very small bubble around him that very slightly pushes him away from walls/floors etc while diving down with ult so that if he does get put into stuck position, he at least slides out instead of remaining stuck.