I have a 100Mbps broadband connection. Over the past one month, the download speed has drastically dropped to 300-500Kbps with Zscaler ON. With Zscaler disabled, I get 10-12Mbps download speed in the same network, for the same file. Tested with file downloads from different websites and the speed is never crossing 600Kbps. Speedtest.net results show ~90Mbps download and upload speeds. Please suggest the workaround for this.
The issue could be related to the fragmentation if you are using tunnel 2.0. If you are using Tunnel 2.0, you can adjust the MTU value and see if that resolved the issue
If that does not resolve the issue, I recommend to open a support ticket for further troubleshooting
Changing the MTU didn’t solve the problem. The problem is not seen with another ISP. Only with one ISP this is observed.