Hey, this map looks like a good submission for an official winter map, I played it a little with bots using the Workshop (good on you for including a nav mesh). I found a couple issues I want to share. I have cl_showpos on in the top right so you can copy the coords into Hammer from there.
You can build on this roof.
And this one.
Stand on this chimeny in front of BLU's first spawn.
These rocks aren't solid, so you fall down them. I think this prop doesn't have collision by default, so you could replace it with a fixed version with snow here:
https://tf2maps.net/downloads/alpine-rocks-fixed-and-mirrored.7645/ I also noticed the cliff flank using a rock prop had blockbullets as well, so you could use this there too in addition to the blockbullets.
Looks like a nobuild that used to block something, but doesn't make sense now.
You can stand behind these walls on this rock. I don't know if this is intended or not, it just might be a rancho relaxo spot or a Soldier hiding to bomb a Medic from here. Graffiti's from Half-Life 2, but you already knew that.
Railing isn't solid.
These bots are trying to drop down from this center square to behind the wall with the dark blue lines.
This RED Engi has a terrible Sentry nest that doesn't cover the point and you can walk past it. I would place a Sentry gun hint somewhere else, or at least at the 90 degree corner if you don't use one already. Also, the control point model isn't solid.
This one's a little inconsistent, but I got stuck briefly walking over this displacement.
You can put "setpos_exact -2561.830811 1622.499878 -27.968681;setang 23.670044 170.342010 0.000000" into console and walk forward as Heavy to replicate it.
These pickups by the first point don't have a patch beneath them. And a nitpick, I prefer (at least on A/D) red patches for ammo and white for health, so when you're burning to death waiting for a pack to respawn, you can stand on the health kit. A lot of small health pickups were slightly higher than the ammo kit next to them too.
At this distance beside BLU's forward spawn, the LOD on this stair model lets you see under the map. The other stairs have black beneath them so it doesn't look like this.
Railing isn't solid.
This little lip in the stair has a gap showing the skybox beside the 2nd point.
A lot of effort was put into this map I can tell, the setting's unique, I like the chokepoints and options each team has. First point's my favorite right now because of the contrasting entry points BLU has to attack from. I have hopes to see this added in December.