SSE

1. Reduced Reliability: Server-sent events are not supported by all browsers and the majority of existing browsers support it only in its basic form. Additionally, server-sent events are not asynchronous, as they wait for the server to send a message before they can display any information—which makes them less reliable than other technologies that rely on asynchronous communication.

2. Limited Scalability: Server-sent events are not suitable for scaling up to large numbers of connected clients due to the additional load placed on the server. This can affect the performance and reliability of your application, especially when there is a large influx of clients.

3. Complex Error Handling: Error handling in server-sent events requires complex and error-prone efforts. The web developers need to take extra treads in order to catch and handle unexpected errors and exceptions in order to keep the application working flawlessly.

4. Security Risks: As server-sent events involve client-server communication, the risk of data interception increases. Moreover, hackers can simulate requests coming from legitimate clients and take advantage of vulnerabilities in server-sent events. This makes the applications vulnerable to DOS attacks.