Even if everyone in your group is trying to put the effort in and not a flake, arranging meetings in our modern world is a pain in the fucking ass, especially if you all have day jobs.
But if on top of that you do have one or several people in the group who are flaky, or lazy, or just suck at doing research you're put in this shitty situation where you either have to nag their ass to work, or just do their work for them. Which then leads to you being tempted to act like a cop and NARC on them to the prof in order to protect your own grade.
The only time I've enjoyed group projects is when the prof set aside in class time to work on it, otherwise it's a shit show, I'll take writing a paper myself over this shit any day.
i hated them to death while on the school, but my job has been glorified group projects for some years already and i found out the main problem with them was that most people usually cared nothing about the actual project. this alho happens during the work but there people care at least for their individual reviews so it's less painful