No output to chat

[SecT0uch]

In my single-player Skyblock world I'm unable to get a /backup command output, while errors work.

/backup help returns nothing
/backup local works but nothing in chat.

It works as expected in my creative world.

Using Minecraft 1.20.1, with Prism Launcher and https://www.planetminecraft.com/project/skyblock-4/

Edit:

Showing error message working as expected

After typing /backup help (or any non-error command), nothing in chat, nothing in the logs

[pcal43]

I'd suspect interference with another mod. Try it with only fastback and see if it works.