I seem to be having the same issue as well. Neither I nor the host have any mods installed, we are running on a 900MBPS network, I have uninstalled/reinstalled, verified integrity of game files, made a backup and wiped all game files with no result. I can join another server hosted by the same person and play my own without problems, it only seems to be happening with the one game.
I checked my logs and I am getting tons of the following errors:
ERR [Steamworks.NET] NET: Could not send package to server
WRN [Steamworks.NET] NET: Tried to send a package while not connected to a server
My log: I had to cut out a ton of the repeating errors because it wouldn't load them all into the link sites
https://jpst.it/2ATBV
Host log:
https://jpst.it/2ATCt