I hadn't heard that theory before, but it's hardly the only NT epistle where there are questions about authorship.
In general, there seem to have been a number of teachers/leaders in that early church and, yes, they did not always agree and there were rivalries at times. The whole conflict over whether Gentiles had to follow Jewish law was one of the bigger ones.
I think the problem we face today in looking at that period and those conflicts is that the church finally, mostly went Paul's way, pushing aside the others. So we often get the Pauline view of those other teachers rather than their own. And the formation of the institutional church after Constantine legalized Christianity led to some of those divergent views getting tagged as heresies or at least pushed even further aside. So we see the writings that the post-Pauline, post-Constantinian church wanted us to see save for the glimmers that archaeological and other finds have given us of non-canonical writings.