When the value of the backpack size is changed and saved, entering the game, the configuration is changed or reset to the preset values.
No matter how many times the file is changed and saved, they always revert back to the default values, even by deleting the json file, reloading the game and modifying the values.

Same issue

I am having this issue was well on the 1.21.1 version. I removed the mods that I had that deal with configs in case they were interfering (Cloth Config, Configured, etc.) but that did not help the issue.

Same issue here, 1.21.1 too

Same

Same issue still today.

persists

I'm having the same problem using v2.8.1-1.21.1. Any time I edit the local client or server config file, it reverts on start to the defaults. Really hope this gets a fix when the dev has the time.

newest update fixes this, configs work now https://modrinth.com/mod/inmis/version/2.8.2-1.21.1