The server crashed

You can try reducing the amount of spawn chunks loaded,
or disabling spawn loading entirely.

Make a backup first.
Change your server software to PaperMC,
try to start the server once (even if it crashes), then stop the server.
A new file has appeared. Go to Files > paper.yml

Now, find and set keep-spawn-loaded to false if you want to disable spawn loading,
or
find and set keep-spawn-loaded-range to a lower value, like 3.

Don't forget to save after editing paper.yml

There is no reason to go back to Spigot

Paper is just a modified version of Spigot. You will keep your plugins, and you will also keep your world if you did not change your Minecraft version.

before you switched to paper, what was the name of your world folder?