This is a common problem experienced by users who connect through a proxy. Proxy servers, although some are very reliable, have stability issues especially when you're using a proxy server with high latency. It happens for all the services, apps, etc., that use proxy servers. If you use a direct connection, then you will see the reliability increases a lot. The causes to this issue can be the speed of the proxy, latency, your Internet connection, etc.
To overcome this issue, use Google Search and look for other proxy servers that are close to your location and offer speed and low latency.