00:09 [Info] [Economics] Saving balances for players...
00:09 [Warning] Calling 'OnServerSave' on 'GUIShop v2.4.48' took 114ms
00:09 [Info] [UI Scale Manager] Saving UIScaleManager PlayersDataFile...

On my server, only GUIShop causes stutter on save. This is not very good as it degrades the flight experience and overall experience of the server. I think the json file is too long and contains inactive items, which causes stutter on save. Is there a way to include only the activated items in the json file?

Why not just remove the data from the JSON that you don't need then?

What you're requesting isn't how things work..at all.

The configuration file only contains the information that you allow it to contain.  The default is just an example - and that's how you should treat every plugin you download if you want to optimize their performance, and create a unique experience that's worth your trouble..

The plugin itself generates the configuration file based off registered information within the plugin to serve as an example for others to understand how to configure the methods.  That's it (for now.)  The LoadConfig class could be rewritten to include detection of items that are only available for purchase AND sell; then have any irrelevant data removed using the SaveConfig class, but ultimately that would just make things harder if you ever decided to add anything, and the slight recode could cause potentially undesired side effects for other server owners.

That said, if you're using something that automatically generates the config for you then it would be on you to either A.  Configure THAT plugin to only generate prices for the items you intend to allow purchase/sell of, or B. configure GUIShop's configuration file to only contain that information.

Either way, it's going to take some work.  Welcome to administration, it's a job when done right.

Even if I remove the unnecessary data, when I reload the plugin, everything in the .json of the config is regenerated, which is pointless. Am I doing something wrong?