I have been using Let's Encrypt on a few domains for a couple of months now, and it generally has been working. I was going through renewing the certs, and for one of the domains I get the following error message (in the returned JSON object at
DNS problem: query timed out looking up CAA for [somedomain.com]
I tried looking up the error, but even Google found zero results (as of this writing). For the naysayers: Yes, this domain (exactly as shown in the error message) is valid and fully accessible and pingable from afar.
There is an important predicament (clue) here, however, as to why this condition has sprung up. I had the settings for this domain set to redirect all traffic to HTTPS when I first tried renewing this particular domain. It seems that LE tried accessing the server at the HTTPS and failed. Since then I have changed the server settings so that the domain is not redirected to HTTPS for the acme-challenge folder. The problem seems to be that LE is remembering that a previous request was redirected, and now it does not want to access the HTTP URL instead. The
challenges.validationRecord has two entries, one at  for HTTP and one at  for HTTPS, so clearly LE is aware that the server can be accessed at the HTTP address as well. Moreover, I can access the validation check file (on the domain in question) at the URL as given in
challenges.validationRecord.url just fine without any issues.
My question is: How do I make LE forget that I tried requesting a cert while having the server set to redirect all traffic to HTTPS? Hence, how do I make LE use the HTTP URL instead?