When you pull up the pip-boy and look under the Data tab you'll find a section which displays the totals for resources at your settlements.

This is damned handy, as it [censored] areas which need attention. Such as, if population goes up, it will show that you don't have enough Water, food or Beds. You can then go in and sort this out.

But I've found of late that these totals have just started going crazy.

Frequently I find Beds, Water, Power even defense drop to 0. I go to investigate, but nope. Nothing is wrong. Correct numbers all around. Nobody has been attacked, everything is normal.

I only started noticing this after I acquired the Local Leader Perks and began setting up provisioner networks. But that wouldn't explain how or why a Defensive value of 50+ suddenly drops to 0.

Anybody else seen this happening?

Yes the same thing happens to me, I've just basically started ignoring the totals in the Pip Boy because they're so often wrong. Mine will sometimes drop to 0 but just as frequently it will show a settlement producing a random lower number, like 5 or something, of a resource that I know it should be producing 65 of. When I go to check it out it turns out nothing is wrong at all and it's still producing 65 like it should.