How to fix memcache on Drupal 7?

Question

Drupal

Good afternoon. There is a site on Drupal 7.36 on VDS with attendance of 300 people/day. It has the Entity cache 1.2 + Memcache 2.2.7 module installed on the server. Recently, some problems began to arise with caching - some sections of the site stopped randomly opening, then some, then others. Either they did not open at all in the form of unavailability for the browser, or an error 502 and Apache's CPU load was 100%.
Transferred to another VDS, glitches with loading the processor disappeared - however, now there is another form of chaotic disappearance of part of the pages with a 404 error. It is interesting that the "missing - not missing" switch occurs once a day at exactly 19.00.
In what direction to dig? There are no viruses on the site, the unix system administrator thinks that the problem is with caching.

Answer 1

The problem was that the domain had 2 server addresses in its DNS records - a very old hosting and a new one where they suffered with the transfer to another VDS! As a result, the site was issued to clients from one server, then from another, causing unpredictable appearance and disappearance of information and orders.

Answer 2

You should at least throw logs or screenshots
.