Weird behavior with memcached authentication

Hi there!

Just to let you know.

Today we encountered a very weird behavior with memcached authentication:


Couchbase server version 5.5.3
XDCR enabled on a static bucket
using a memcached bucket as well
same user with application access on memcached and static
java client 2.5.9 (same issue with 2.7 latest)
we just bootstraped our 3 nodes cluster with xdcr feed from a on premise datacenter to a new gcp datacenter


everything goes smoothly with the static bucket but memcached bucket leads to the following behavior:

client side

2020-01-23 15:31:45.332 [cb-io-1-9] [ WARN] c.c.c.c.RequestHandler - Received Error during Reconfiguration.
com.couchbase.client.core.endpoint.kv.AuthenticationException: Authentication failure on Select Bucket command

server side (memcach.log)

authenticated as <legit user> 
connexion reset by peer


set up the memcached bucket as a static bucket (delete then recreate)

everything works just fine (we just wanted to prove this was a memcache issue)

Rolling back to a memcached bucket (delete, recreate)

everything works (issue fixed)

Can you explain what happened ?