"Another key element of online racing, either in a league or quick race multiplayer environment, is the ability for users to proudly display their own custom or downloaded liveries. Since the introduction of the refreshed UI in rFactor 2 this feature has taken something of a back seat, however we are currently in the process of reinvigorating and refreshing how skin transfers are handled within the UI, with much improved performance and functionality set to be introduced in the near future. We are looking to offer up a much simplified and clearer progress bar and status icons around skin transfers, although this enhancement is still very much in the early stages of development, we expect it should vastly improve how skin transfers are handled within the simulation."
Let's hope that this fixes it, in the meantime... I might implement that for "my" club races.