So this is a really wicked feature and concept, so far as I know, only available in Norway map...
Didn't think I was making it past wave 15, this level seems harder than the others.... but I got the Tesla and the Panzerfaust luckily around wave 13 and 15... upgrade them both as I usually do... then going by the upgrade weapon bench i notice in this level you can KEEP upgrading for higher prices...
So I upgraded my Tesla twice total, works fine (not sure about the 3rd upgrade)
but the panzerfaust... glitches after the 2nd upgrade, like doesn't work at all glitches.
It goes to a 3 rocket shot with 30 loaded ... however I shot the first 3, then it just wouldn't reload not only (staying stuck on 1/30) ... but just completely didn't work at all after that, not even for a single rocket shot.
love the idea though... once this is fixed, makes me believe I can get to waves 25-30, maybe even beyond.
Thanks again for hearing me out, since I'm so full of complaints hahaha ^_^

Side note about Norway: I've also had the game just totally cease up on me twice so far in about 4-5 times playing this map in the past few hours... Didn't really get this at all with other maps.
Have you had similar feedback about this particular survival map?

Damn, this Norway map is kind of full of bugs.
1st try today, get to wave 11 and then enemies just dissapear completely (a mutants wave) and fails to progress me to the next wave, leaving me stuck there.
Frustrating tbh to waste the time only to get stuck by a bug.