A user on reddit posted about his friend being banned from GTA Online after having completed 3,331 hours in the game. That is a lot of time. That’s more than 138 days on playing GTA Online in real time.
Now some of these bans looks really stupid when it comes to GTA Online. Players actually do spend a lot of time doing missions and collecting items and for Rockstar to punish the player like that without them having a chance to appeal or explain themselves is really bad.
Some players are giving them advise as to contact the social club website they can also check on twitter with the support team about what happened. It is likely that the user might have tried some glitches or tricks which were not allowed in the game due to which he got banned.
Since he was a PC player this is very common in PC players. Also some other player who was playing along with them might have been trying some glitches which could have given them some benefit as well in the game due to which their user ID might have been flagged.