maybe somebody got into your account or something

Looks like someone was in your account my guy

Well seeing as I was logged in the whole time and have an authenticator, no.

maybe it was somebody in your family and somebody sneaked in
or from the window

1.) Check if you are logged in on the correct character. To check, press C and take a glimpse at the character name in the upper left corner of the screen.
2.) Don't use third party software like Pindle bots, they may be unsafe and compromise your character.
3.) Your account may even be compromised. Check your computer for viruses and keyloggers and change all passwords (on another device) as soon as possible.
4.) Your gear seems to be broken. Repair it at a blacksmith in town (e.g. Charsi) to make it usable again.
5.) Sometimes people sell their items to vendors accidentally. If you are still in the game, you can check the vendors in your act for your items. Unfortunately, they will disappear after an inventory refresh.
6.) Contact Blizzard customer support to get some help to solve the issue if the above doesn't fix the problem.

Hope that helped!

You woul think with all the technology we have today, being able to instantly save ~30 minutes of prior gameplay with nvidia, someone would have some fucking video proof of it poofing

Someone did actually post video evidence of it occurring, but the title of the video was in Korean so I can't fucking search and find it. A link was posted in one of these "item poofing" threads

Most likely reason is explained in this thread

https://forums.d2jsp.org/topic.php?t=88954805&f=148&o=100

This has actually been happening over the past couple days you just gotta check the official forums. It does seem to be linked to crafting a ton of items though.

you COULD back up your offline characters.. though it is a pain to do so of course all the time