Issue Description: Getting this warning when the server is running. It doesn't happen often but it still occurs. Starting to get annoying seeing it.

• Dynmap Version: core=3.1-beta4-421, plugin=3.1-beta4-421
• Server Version: git-Spigot-17d78db-5c77bd2 (MC: 1.16.3)
• Pastebin of Configuration.txt: https://pastebin.com/FqBuWtHB
• Server Host (if applicable): McProHosting
• Pastebin of crashlogs or other relevant logs: https://pastebin.com/APEr5TCY
• Steps to Replicate: Server has to be running and over large periods of time this warning comes to be

• I have looked at all other issues and this is not a duplicate
• I have been able to replicate this (not the first time I've been seeing this warning)