ATM-7
Minecraft 1.18.1
Modpack version 1.0.0

The diamond backpack was from the Sophisticated Backpacks mod.
I started carrying all my ores/valuables in my diamond backpack.
I also just started doing the blood magic mod.
I had my backpack on my hotbar.
I was using the sacrificial dagger to put blood into the blood altar, when I wasn't paying attention to my health and killed myself with it.
I came back to the gravestone and used the key on it and (I think) I got everything back.
I only noticed like 5 minutes later when I couldn't find my backpack for some materials. I know that I didn't drop it bc I didn't drop anything on the ground for awhile so it shouldn't have despawned. I looked around the common places I'm usually at to see if I placed it unknowingly. I looked through my chests to see if I put it in there by accident. Nothing... but tbh, I wasn't paying attention to everything, but where did it go???
I don't know if it was a glitch bc of the blood magic combined with killing myself with the sacrificial dagger along with the gravestone mod. But that's the only logical conclusion that I could come up with at the time or even now while typing this.

So, in the end, along with everything that I put in my backpack, the backpack disappeared.

Did you check your curios slots (icon to the right of your player model in your inventory) to see if the backpack got placed in there?

Did you check your curios slots (icon to the right of your player model in your inventory) to see if the backpack got placed in there?

You were right, how is that even possible?
I'm assuming that it was placed in that slot when I died.
Thank you for clearing this up for me.