In which file did you encounter the issue?

/appengine/flexible/memcache

I commented out memcache server and uncommented: USE_GAE_MEMCACHE

On deploy and gcloud app browse I see:

error 3 from memcached_get(counter): (0x14b9130) CONNECTION FAILURE(Connection refused), host: localhost:11211 -> libmemcached/connect.cc:156