I found out that we had some bad chunks in the Creative world. The only solution I could think of to fix the Creative world was to use a tool I found which lets me port it to Bedrock edition. Then I took the Bedrock version of that world and ported it back to Java. That forced it to regenerate all of the chunks and it seems to be working great now.
In other words, the crashing that was happening over the past few days should now be fixed. Everything seems to be running great. I currently have Dynmap rendering the worlds so that'll slow things down a little for the next few days but it should all still be very playable. Speaking of Dynmap, the new URL can be found here:
http://vizzed.co:8123/
For those who don't know, the address to be used to join the Vizzed Minecraft Server is:
Vizzed.co
I have just a few little things left to do with the server before I make an official thread and announcement informing everyone that it's back up and running great. One of those things includes getting the site to communicate with the server properly again (like showing who is online and stuff).