Or is it just during winter the spawn rate is down maybe?

Cause for me it's usually around 40 but level 6 and 7 on the forest explore have both spawned less then 20 enemies on the map these past few days..

If that's what you mean.

In the winter all the terrains, except the jungle, will have less prey, it's not something that only happens in the forest territory. The jungle territory is the only territory not affected by winter.

But other than that no. The prey count and enemy count will be random each new level, and will be different every time you replay a lower level.

Higher levels overall will normally have more prey, and enemies, than the lower ones do though.

Winter shouldn't affect the enemy count, it only affects the amount of prey you'll find.