Perhaps you are just using a low-quality proxy server. A more anonymous option is shared proxies with limited access. If public proxies can be used by as many people as you want, which reduces their stability and speed of operation, then the text is taken from a chic proxy with a border with unlimited access, only those who have paid access to it can connect. Connection to such a proxy server is carried out using login and password authorization or is limited to binding to a specific IP address. Try using turkish proxy.
We understand that firewalls create significant security barriers. However, they can sometimes affect the connection of VPN clients. Most of them will tend to slow down your internet connection, causing VPN disconnection. They can also create a VPN activation process under certain conditions. Perhaps your situation is exactly like this. But if you have checked your computer for the absence of VPN programs, then this is quite strange. Even when I used the Turkish proxy for work, I did not have such problems.