Maximum backpack weight is 400

p90s weigh 10%

you have 50 p90s in a stash

try and take one out

all of them come out

only get 41 p90s (one in ur hand, 40 in backpack)

rest of p90s disappear into lala land (nowhere, not even on ground)

this is a problem when you are already carrying rocket launchers in backpack since they weigh substantially more

easy fix

make it like body armor, where you can only take one out of the stash at a time

Hold Ctrl to take only one item
(Had the same issue and pasik told this)