This is it. I modified a website and added a button to jump between http and https on the homepage. The homepage test is OK.
(Homepage, gray icon is http, green is https)
(Content page, switch to https, it will be forced to use https access, only clear the browser cache)
Me I thought it was definitely a browser cache problem, and then I set up not caching on the program and server, but it still didn't work. Is there any solution?
Everyone, thank you for your attention. I have discovered the reason. It is because HSTS is turned on. Just turn it off.