This is the exact same problem i am having, the lag literally looks exactly how mine does. I have a good PC and 80+ upload speed, i believe by watching a lot of videos and reading forums that my settings in OBS are correct but my stream just lags, I did one stream playing Sea of Thieves and it went quite well apart from the video quality being stuck at 720p, after that i tried it to change a couple settings to get a better quality and it must have done something because after that my streams were either slideshows or had lag.
Here is the original stream which didn't have any lag but a couple frame drops :
https://www.twitch.tv/videos/221842065
and the test streams at 2000 Bitrate:
https://www.twitch.tv/videos/222943084
and then another test stream back at 3500 bitrate still with lag:
https://www.twitch.tv/videos/222948971