Mod Version: 0.1.5c
Issue:
The Incinerator, which is from a mod called L_Ender 's Cataclysm, can't be fully modified by tweaking weapon_items_flat.json. The modification of many Attributes can't work successfully. With only a few exceptions, such as Damage Class.
Here are some screenshots.

Got it. So I just tried another open source mod called Epic Knights: Shields, Armor and Weapons, and found that none of changes made by IDF to Epic Knights' melee weapons could work successfully.
Here is the source code site of this mod: https://github.com/Magistu/Epic-Knights

I checked the mod in question. Since there seems to be little to no information on the curseforge page, and no source code provided it's very difficult for me to figure out for sure what is going on. My guess is that the mod doesn't implement attributes the vanilla way which is what IDF tries to modify.

Actually another person commented with this issue a while ago. This mod also uses a strange custom system for attributes. At some point in the future I may look into a workaround but currently it isn't a priority as not many mods do this.

Okey, focusing on the present is always a good idea, and I'm also looking forward to the arrival of that day👍

Newest update fixes this issue. 👍