During the admin ui port for memcache, memcache_bins and memcache_servers settings were erroneously added as config instead of using the MemcacheSettings service via settings.php. While the README suggests using settings.php, servers do not correctly load unless you use the config object.
Starting with 8.x-2.6, settings from the memcache driver are now correctly using the MemcacheSettings object. These config settings didn't have a correct schema either, so removing them will clean up any schema errors you may be seeing on your site. If config is set, it will overrule settings.php for the 2.x branch.
Starting with memcache 3.0.0, references to the config object will be removed. If you're using the config object, be sure to verify they match the memcache settings in settings.php instead of config.
Before:
memcache.settings:
memcache_bins: []
memcache_servers: []
After
$settings['memcache']['servers'] = []
$settings['memcache']['bins'] = []
