When you die from an explosion (e.g. Creeper) the grave doesn't generate and all of the contents are lost forever.

I tried setting Last Resort to set_grave instead of drop_items in case that'd be the reason (maybe it tried placing the grave after the explosion removes the blocks?) yet it didn't solve the issue. About this, I left Generate Block Under Grave on as default as well as the other related settings.

System info:

• OS: Windows 11
• Minecraft Version:1.17.1
• Mod Version: 1.1.6

Fixed in 1.1.7
Thanks for reporting!

Also if you would have a similar problem again, you can use the /retrieve_grave command