Service Unavailable message on a single, upper level page
I am also starting to see, at various times, "429 Too many requests" error pages from any page visit or attempt to follow an action like a save during an edit session. Could it be we are being hit with a DoS attack? Server logs from the hosting provider do not really indicate this; that I can see. No unusual or heavy load. It is an older "shared physical host" service. Beginning to get very frustrating. I have not reached out to the hosting provider as it takes hours to walk up the chain to find someone who really knows what they are doing.
UPDATE: This may have started after turning on cPanel Site Quality Management. It appears they pound the server too heavily. I turned it back off and have not been seeing Too Many Requests any more. But still seeing the Service Unavailable message consistent on those two pages. Without fail.