This redirect is typically generated by Fastest Cache. I would try to clear, then deactivate completely. Then, activate again. In most cases this will solve the issue.
If not, you could try to move the http to https redirect to the top of your .htaccess. If https is no problem, it might be solved by making sure the Fastest Cache .htaccess rules only kick in after the redirect to https has been made.
Wanted to test it a bit more before replying, but everything seems to work fine after disabling and re-enabling fastest cache. I noticed the problem came back after I reuploaded the mysql database for one of the websites, but re-enabling fastest cache again fixed the problem again. If the problem comes back after other updates I will try the other solutions you provided!