we installed the version of this mod for 1.14.4 and get an error message that the mod failed to load, with a reference to net/minecraftforge/registries/DeferredRegister

(I don't know what that means and have never gotten this error message before)

Thank you!

You need to post your /logs/latest.log file when this happens.

The file gets wiped and rewritten to each time the game is launched so it needs to be posted immediately after the error happens.