What causes VPN disconnections?

Even the best VPNs can experience connection drops from time to time, and no technology is perfect.Disconnection from a VPN can occur for a variety of reasons, including:
You are connected to a weak or overloaded Wi-Fi network, such as in a cafe, hotel, or airport.
You switch from Wi-Fi to mobile data or to another Wi-Fi network.
Your computer shuts down.
Your VPN connection is being disrupted by an antivirus program or firewall on your computer (in this case, whitelist your VPN software).
You jump from one VPN server to another, or you quickly switch servers and exceed the number of simultaneous connections allowed by your VPN provider.
You are making use of the OpenVPN UDP protocol, which is less reliable than the TCP protocol (if you notice that your VPN is dropping, switch to TCP).
The VPN server to which you are connecting fails.
The VPN app stops working.