I have this error happening for the last 2 months - I am not able to upload qty/price report and if changing data manually facing the same issue - connection lost.
For 30min+ the connection with website in our office is lost although I can still preview the website using my phone data.
I have also tried uploading data at home to make sure there is no office wifi issue but have exactly the same result.
All the party involved: server provider, it support and website developers cannot resolved the issue.
My website is www.1855thebottleshop.com
It will be helpful if you can chack the webserver error log or even the Magento's logs to try to find a clue about the error.