I wrote this in a comment of already closed issue, so, just to make sure, that you notice this:
The new command /rp debug-item doesn't do anything, if you don't have permission. (I mean like without message "You don't have permission to do this")

And found out, that if you don't have flag block-transform set to true in claim, you can't place anything from mods.

Happened with RedProtect build 310 and Mohist build 439

Its all spected. As a debug command, the players should not see this command and will show the help info instead. block-transform handles all blocks transformations, then can handle a lot of things and need to be used with caution. If the mod itens are treated as block transformations, its not a redprotect issue. This flag handles BlockFadeEvent.

I recomend to use the flag block-transform after end the works on that region.