When you force push a PR, Gitlab shows the changes from the last push. So it also depends which forge you use. I could see that working less well on Github or simpler Git forges
Yeah I don't have much experience outside of GitHub for team projects, so maybe gitlab works better. For GitHub it just gives up and claims it can't give you diff since the last review
GitHub is basically worst in class here, it’s true. Some forges are slightly better, others are way better. It’s so sad because I like GitHub overall but this is a huge weakness of it.