There should be a warning for the purple crystal boss battle before entering the portal. Or maybe you have to press a button to use the portal.

i have to make laps of the map trying to find what crystals are available to grab and the ones that were weren't the material i needed (600 iron needed for 3 machines). really all of them should be up with maybe a few minutes cool down. I played for an hour and just had the uranium gen to show for it.

More in depth edit:
Anything bad I have to say about this map is just about materials. i want to love this map but there are some glaring issues with the mechanics. its such a colossally cool concept for zombies but its done really poorly here with some really small mistakes. Everything in this map revolves around collecting materials and that's fine, however you'll quickly find that they're incredibly hard to find as only a few can be up at a time and some even spawn in zones you cant get to yet taking up a potential spawn. Playing this map solo also feels like a choir as the fewer players you have the less materials you have overall as only 1 person can get them instead of 4 at a time. The fix to this in the map are the generators but they come at an insanely hefty price tag to build (save for the copper gen) and only the copper and cobalt gen are useful for items in the early game. Points are essentially useless with the exception of a few decent wall buys and powering the gens but with their very high cost to build you wont be using them fully until later. Surprisingly with wood and iron being some of the most commonly needed materials you wont find a generator for them, i don't know if its because they're "earlier" resources but with the way that only a few crystals can be in at a time they become just as rare as the others.

Suggestions to fix materials:
-all material spawns available to be collected with a 3 minute cool down for each
-lower cost to build generators specifically uranium, platinum, and cobalt
-add wood and iron generators
-add more than 1 way to turn points into materials
-have at least 1 of each type of material available at all times
-higher material yield at lower rounds

thank you for coming to my ted talk