"To date, we have not received notification of other users encountering this kind of problem with this game’s achievements"
Plenty of people have told them about this issue, what they are saying is just a massive lie. People have been reporting this problem to them since the Dreamcast collection was released.
SEGA your customer support is awful, just like most customer supports.
Sorry guys but you may as well just give up, this won't ever be fixed because they just don't care.