Upgrading Drupal

When our website was upgraded to 7.65, many users experienced loss of content.  There was no pattern, the missing content seemed to be quite random.  The problem was very widespread and the release was backed out.

I have found that the website has subsequently been updated with releases 7.66 and 7.67, but 7.65 has not been applied.

We obviously don't want the website to be vulnerable and are trying to find out:

I performed the most recent core update on my site's localhost via composer. The update worked fine.

I then committed changes to git, pushed it to my github repository and then git pulled it to my live server (shared hosting/cPanel).

That caused my live server to go white, with no pages loading anymore and it also stopped drush commands from working in Terminal (logged in via SSH) on that server.

I restored the Server to previous day backup and site loads fine again with drush commands running OK again.

I tried it again but went the extra step of:

Hello, a few weeks ago I encountered the problem of "Drupal is already installed". No suspicious activity was done before that. During my research, I realized that it was due to a bad installation. I redid the installation following the drupal guide. For two days, the problem has reappeared. I admit that I can not find a tangible solution. Indeed, I already have a site on it with the theme TheMag. My concern is to recover my site with the data: return to an initial situation. I am at version 8.7.6
Thank you for your contributions and indications

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