I have detected an oversight in the guardvillagers mod. Vanilla villagers come with different variants for the biomes. One of them is snow variant wich is spawning in these biomes:
frozen_ocean deep_frozen_ocean frozen_river snowy_beach snowy_taiga snowy_taiga_hills snowy_taiga_mountains snowy_tundra snowy_mountains ice_spikes

The problem with the guardvillagers mod is that the snow variant doesn't spawn on frozen ocean and perhaps on the other biomes too (i didn't check all of them).
You should definitely consider fixing it.