It's pretty par for the course that when a new version of GTA Online comes out, a wave of bans come along with it, as Rockstar patch out exploits and improve their anti-cheat mechanisms. Unfortunately, this process can be a little too thorough, as significant backlash from the community shows a lot of players protesting their innocence after the "Southern San Andreas Super Sport Series" cause a wave of bans.
And it could very well be the case that these players are innocent. The bans are centred entirely on the PC version of the game, and could very well be related to users with mods installed on the main GTA V single player side of the game.
The Southern San Andreas Super Sport Series is a new update that adds stock car vehicles and new outdoor racing tracks to the game. The update also addresses a well-known car selling exploit, and this may be another source for the bannings.
This post on Reddit explains how the ban wave appears to be affecting innocent modders, and that innocent modders are being singled out with bans without an explanation.
While nobody has any exact causes yet, there is some speculation that the bans may be related to a very popular menu mod, and the Turnables editor for GTA V is also apparently a potential cause, with the developer of that mod posting a fix is in the works.
In the mean time, if you plan on playing GTA Online with the new update, we suggest disabling mods just to be on the safe side.