This blog is hosted by Bluehost. Recently, new posts were not showing automatically when published. I changed the cache plugin from W3 Total Cache, one of popular WordPress cache plugins, to Hyper Cache. However, the issue did continue.
I suspected that the culprit might be server cache. I contacted Bluehost and asked, "How can I clear the server cache by myself?" Since I use the Bluehost VPS plan, I can access SSH with the root privilege.
They suggested to use the following command to clear server cache:
sync; echo 1 > /proc/sys/vm/drop_caches
I could clear Ram Memory Cache with the above command.
Unfortunately, the issue did not disappeared even though I cleared server cache.
I finally found the reason: the culprit was Browser Caching.
When I unchecked "Allow browser caching" in Hyper Cache, the cache issue disappeared.
If you have a similar problem, please try to disable "Browser Caching", which might resolve the issue.
Just for your reference: Shared Hosting accounts are not allowed to access SSH in most web-hosting companies including Bluehost. However, Siteground allows their Shared Hosting account users to access SSH.