Upgrading Couchbase Server Docker from CE6.0.0 to CE 6.5.1 fails

I am running a single node dev system under couchbase server 5.1.1CE with the official docker image. I now wanted to upgrade to 6.5.1CE. I did so following the upgrade guide be first upgrading to 6.0.0CE and after that upgrading this to 6.5.1CE. I do upgrade a single node by just shutting down docker, change version und startup docker again.

The first step from 5.1.1 to 6.0.0 works fine and all my existing buckets are migrated. But the 2nd step from 6.0.0 to 6.5.1 fails at warmup. The messages in babysitter.log show:

memcached<0.114.0>: 2020-06-27T13:00:56.812806+00:00 CRITICAL () Warmup::createVBuckets aborting warmup as vb:2 datafile is unusable, name-spacing is not enabled.

multiple times for all buckets. I took a look at the kvengine source and only found a comment, that collections and repl needs “namespace” as an attribute in the vBucket.

So is there a was to upgrade to 6.5.1CE while keeping my existing buckets? How would I add “namespace” to a bucket in 5.1.1 or 6.0.0?