Delaweare (Doom II mod) - 100% kills 100% secrets

I get 100% of the kills and 100% of the secrets, but no matter how much I tried, I could never find 100% of the items. The closest I got was 98%, meaning there is one item that I couldn't find. I've tried turning on no clipping mode before and still couldn't find that one missing item.

The creator of the mod announced it on Doomworld here:

https://www.doomworld.com/forum/topic/69215-delaweare-release/

And provided the following link to download the mod:

http://spaceisgreen.nl/delaweare.htm