Hi!
I'm having issues with ChestShop and maybe memory leak!
https://pastebin.com/9EQzPxUD

ChestShop v3.9.3-1.12 (build 20)

Unfortunately without knowing the shop setup and item information in it it's near to impossible debugging this as the log doesn't really contain any info besides that it failed to create a config (which is most likely the metadata storage system which generates a yaml config to save the meta data). So you either have an item with too much data or simply a bug in your old server version which leads to it failing to serialize certain item data.

Both of them probably lie outside of the responsibility of this plugin but I've gonna leave this open in case some more information turns up and maybe there is a way to prevent this in ChestShop itself.

Please provide the rest of the information requested in the issue template. Especially your config, your full log (yours seems to be cut off) and some info about the shop setup causing it as well as information about the player interacting with the shop with what item.

Config:
https://pastebin.com/8htZRvce

Full error:
https://pastebin.com/GWbgLsab

Version:
This server is running Paper version git-Paper-1618 (MC: 1.12.2) (Implementing API version 1.12.2-R0.1-SNAPSHOT)

Do you mean the database files?

No, I mean the setup of the shop which's creation caused the error and the item used for that shop.

and the error tells which item and shop is it?

Unfortunately it doesn't.

So what should I do?

You'll basically have to find the shop and the item that caused this. This might even be a bug in your outdated server software itself with how item data is handled as there are a good chunk of issues in these old versions and I highly recommend updating to supported versions.