I am having a rather strange issue with my current character. She appears to have a "hidden" 70lbs of weight on her that doesn't seem to come from any gear.

Her current loadout is as follows:

Trail Carbine (5.5lbs)
Brush Gun (5lbs)
1st Recon beret (1lbs)
Space Suit (7lbs)
Doctor's Bag x2 (2lbs)
Stealthboy x3 (3lbs)
Weapons Repair Kit x2 (2lbs)
Caravan Deck- 1lbs

That's all items which have weight. There are currently no quest items in my inventory that have weight. But her inventory weight? 88lbs! I've tried unloading all weight-having gear off of her, and her "empty" weight is in the high 70-s.

What the heck?

For most of the playthrough, her loadout was in the high 30-s- low 40-s. I didn't notice when it changed but it must have been during one of the shopping trips.
Is it a bug, or is there some kind of explanation? And if it is a bug, how do I fix it?

Do use the workbench a lot to break things down into lead? Lead has weight....it's just too low to show on the screen so it'll say 0.0 weight but it does weigh something so if you have thousands of it....There's other stuff like that too, like some of the plants.

Yes, come to think of it I did use the reloading bench a lot recently, converting ammo into handloads. Thanks. Will check it out

Is it in hardcoe mode? If it is, the ammo has weight too.

Nope, not hardcoe. But Lady Crimson was right on the money; I had a LOT of lead, and once I offloaded it the weight came down to reasonable amounts.

It's the lead, I had 124 pounds the other day.