Having connection problems

Let me start off by saying that this might not be exactly a paper issue but the only reason i run my own server is to host a paperspigot server so any help would be nice.
I’ve been hosting for over 2 years now and recently I have had a problem where my server very rarely, around 2x a day just closes the connection to everything (all players on the minecraft server, putty and my ftp connection). After that happens I’m unable to connect back to the server with any of the previous methods for ~30sec. Some people on the minecraft server sometimes just get randomly disconnected as well. So far I have reinstalled my server multiple times, switched ports on my network set up, tried different routers, tried just directly plugin the server into a modem (which I’m currently doing), and factory resetting all my network devices multiple times.
My server is a ubuntu 20.04. Firewall on the server side is disabled due to this being a private server.
One of my friends completely can’t stay on the server for less then 1-8min before getting disconnected (although I’m guessing its more of her side of a problem then mine.)
The screenshot bellow is the message I receive when everyone on the server gets disconnected at once.