I'm on my second playthough of Dawnguard, and I cannot get these two to spawn.
Just like on my first character, only ice wraiths spawn on the lake.
I'm at the point where I'm supposed to go learn Dragonrend in the MQ, and the first character had already finished it.
Level 42.

I've tried entering the lake from both directions, walking, running, sprinting, standing still, waiting in a different cell for multiple weeks to get the area to respawn, tried finishing the Dawnguard quest and coming back.
I've also tried disabling all my mods, and even spawning the stupid dragons with the console (they won't dive under the ice and are fairly buggy when summoned this way).

Does anyone know what causes them to spawn or not spawn?