We have 5 Cloud HTTP sensors in place pointing at the landing pages for our customer facing sites as part of a layered set of checks; other layers include non-PRTG held scripts on external resources.
Since 13 July 2018 23:02:53 we have been seeing multiple reports of: "The returned JSON does not match the expected structure (Invalid JSON.). (code: PE231)" triggering warnings and then subsequent down notifications in line with our configuration. There seems to be no consistent pattern to the failures and it seems to only affect 1 or 2 sensors in turn.
These sensors have been in place for 490 days without this issue, and no changes have been made to our external firewall configuration, our web server configurations or the landing pages themselves.
The available KB articles, e.g. this don't seem to apply in these circumstances.
Is there a change currently being made to the Cloud HTTP sensors from PRTG's end?