I did note the variance in a settlement management mod (why it's not a part of the core is beyond me) that 17 beds would be sheltered in one check, then only 3 the next time. Figured it was yet another Bethbug. I've also noticed that even if I assign a bed it'll be unassigned (red) during the daylight hours and the settler I assigned to it would not return to that bed at night (tested this with a 1 person settlement and 5 beds - the guy was assigned a bed, but picked a random one each night). The whole settlement thing, IMO, is a massive Bethbug.