/gamerule has stopped working on a server I manage after seemingly unrelated changes

Question

Basic information: the server is running Spigot 1.16.5 on Shockbyte Hosting.

/gamerule has completely stopped working. Interestingly, it's still shown as an autofill when I type /game, but when I enter /gamerule, I get:

Unknown or incomplete command, see below for error
gamerule<--[HERE]

It was working perfectly (literally used it just a few hours before) until I started the server after making the following updates:

• Added:

  AntiCreeper.jar, Parties-3.0.4.jar, MythicMobs-4.11.0.jar, waystone-master file folder (Later deleted; kept here for consistency, this one was from GitHub), Quests-4.0.2.jar

• Changed:

  Default config: bukkit.yml: spawn-limits: animals: 10->35, ticks-per: animal-spawns: 400->375

  EnchantsPlus: disabled-enchants.yml: excavation true->false

I have no idea what I did wrong, I've made changes like this at least ten times before. The one time we had a similar issue was with SkillsPro, which had config that broke for no discernible reason after the change of a single number; when that happened, the same occurred (shows up in autofill, gives immediate error after entering).
So far I've tried manually removing or reverting each file one-by-one with a server restart after each with no luck, and Google has been no help (that I'm able to find, at least).
I'm very new to running a server, doing my best to learn quickly - apologies if I've missed something small or done something stupid.

Answer 1

/gamerule sendCommandFeedback was set to false.
This has seemingly fixed the issue - /gamerule on its own still appears broken, but specific gamerules give output now.

So, if anyone in the future comes across this issue, this may be the solution.