On some versions of WordPress®, there may be no appropriate official ISRG Root X1 root certificate needed for our products to work properly. This situation is caused by letsencrypt.org has started using this new root certificate.
Typically, this certificate is included in WordPress root certificates byndle and downloaded with it’s updates. But in case of its absence, the system does not recognize our site as trusted and shows unnecessary warnings that interfere with users’ work. And you need to download it from the official WordPress repository and replace local file \wp-includes\certificates\ca-bundle.crt manually.