I have tested it many times, after you die in the RaidableBases area, the items in your backpack will disappear.

Do the contents of the backpack fall into a bag where you die? Raidable bases has config options for backpacks dropping on death. You might have previously set these to true.

• Backpacks Drop At PVE Bases (false) - Will drop a backpack on death, even if explicity disabled in Backpack configuration (requires Backpacks 3.4.0 )
• Backpacks Drop At PVP Bases (false)

WhiteThunder

Do the contents of the backpack fall into a bag where you die? Raidable bases has config options for backpacks dropping on death. You might have previously set these to true.

• Backpacks Drop At PVE Bases (false) - Will drop a backpack on death, even if explicity disabled in Backpack configuration (requires Backpacks 3.4.0 )
• Backpacks Drop At PVP Bases (false)

When you enable these options, Raidable Bases takes executive control over dropping the backpack, and does not respect any keep-on-death config/permissions from Backpacks.

Yes, I checked the RaidableBases config file and the Backpacks Drop At Bases option is on by default