Turtles mate just fine, lay eggs, however after a few MineCraft days the eggs simply disappear and no baby turtles are found. I have tried this several times each time protecting the eggs so zombies can't get to them by placing fences around the eggs.
The eggs do indeed hatch in 20w18a as usual, which I have just checked in-game. You might want to provide a video of turtle eggs disappearing or try playing on peaceful and enclosing the eggs in a room, which other mobs cannot enter. If the issue remains the same, your assumption might be true.