Updates fix bugs and occasionally introduce them. The difference between a routine update and a lost evening is almost entirely about what you did before pressing restart.
What to do
- Back up first, and include the configs
Not just the world. A plugin update can rewrite its own configuration file into a new format, and that change does not reverse when you put the old jar back.
- Read what changed
The release notes say whether the config format changed, whether a dependency was raised, and whether the update is for your Minecraft version. Two minutes here saves the rest.
- Replace the jar, do not add it
Delete the old jar before uploading the new one. Two versions of the same plugin in
pluginsis a reliable way to get behaviour nobody can explain. - Update one at a time
Especially across a major Minecraft version. Updating twelve plugins at once and finding a broken server means you no longer know which one did it.
The server starts, the plugin loads green, and the feature you actually use behaves as before.
Do not update on the evening your players are online. Updates are for quiet hours, so that if something needs rolling back, nobody is standing in the world while you do it.