There are many causes of "Unexpected response from server - please try again or switch off JavaScript" error.
To know the exact cause of the problem, then open your browser inspection tool, then click on console, and then under console check Response. You will see the exact cause of the problem.
If your Q&A website is in the same directory or sub-directory of a website using the WordFence plugin, then check the tools section to confirm whether WordFence is blocking the action that you want to perform (posting action). Also, enable WordFence option to scan files outside WordPress directory.