SharePoint search has been working fine – all of a sudden we may notice the search has stopped working throwing this error – “Unexpected response from server. The status code of response is ‘500’.”
This is due to high memory utilization in the SharePoint server. Login to SharePoint server task Manager -> Performance -> Memory . There we can see memory utilization is closed to 100 percent, so release some memory by closing unwanted or un necessary application which is consuming more memory. Then this will get fixed automatically.