Thanks for the response. I performed all of the steps you mentioned. Earlier today I got a response back from my host and they had been doing #4 (host caching). I’m not sure why they would do this, as this is a premium service from them (for use on high volume sites, for which I am not). After the cool-down for caching was reached, my sites started returning to normal function.
Thanks again for adding #4 to the list of things to check. Yours is the only list that I saw in searches that mentioned it. Consider this one solved.
