I digged a bit deeper, it seems a couple of DLC cars have lost their divisions :
1977 Holden Torana A9X (missing from Classic Compact)
2014 Maserati #35 M.Calamia Swiss Team MC Trofeo (missing from Modern GT Racing)
1980 Lancia #31 Lancia Corse Beta Montecarlo Turbo (missing from Early GT Racing)
2014 Mazda #70 SpeedSource Lola B12/80 (missing from Endurance Prototypes)
2014 Toyota #8 Toyota Racing TS040 HYBRID (missing from Endurance Prototypes)
This clearly looks like a bug to me.