Connection issues aren't very specific, which means it's impossible to know what's causing the problem.
"Lost connection to CoopNet!" or "Cannot connect to CoopNet!"
* Make sure your router isn't blocking the connection to CoopNet.
* Your computer could also be interfering. Try disabling your firewall and antivirus. Also, make sure you don't have a VPN enabled, as those don't work on CoopNet.
* Make sure you have an active internet connection, and that it's able to hold a stable connection. Connection speeds also play a big part in this. If your speeds are very slow, it's likely that a connection won't be established.
* Try changing your DNS and flush your DNS cache. Sometimes that could fix random disconnects.
* Network congestion...