Strange consistent log notices. Where do they come from?
Since it's coming from include_once I suspect you have two civicrm.settings.php files.

The correct location is sites/&lt;default or example.org&gt;/civicrm.settings.php

If there's a file in sites/civicrm.settings.php, rename or remove it and see if that ends the errors.

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EDIT: OK, having reformatted your question I can see the file path isn't actually sites//civicrm.settings.php ... StackExchange was hiding your sites directory because of the angle brackets.

SO - either you have two files (eg sites/default/civicrm.settings.php AND sites/example.org/civicrm.settings.php) OR your site somehow include_once's it after it's already included (?).

Let's use grep to look for files which define that constant:

grep -riE '^define.*CIVICRM_MEMCACHE' /path/to/site/root


If that identifies multiple files with this constant defined, then you probably want to eliminate one of those files. If it only locates a single file, then you may need to dig further to identify why that file is being included twice ... especially when the second time, it's being included using include_once :)