Github's code review tool is uniquely bad. Notably it presents every comment as blocking and requiring sign off - even a "Glad someone cleaned this up! <thumbs up emoji>" needs clearing before merge.

It also has some UX snafus that cause reviewers to write a number of comments and then forget to publish any of them, leading to a lot of interactions along the lines of "I thought you were going to review my PR?" "I already did?"