@mat01, Thanks for making this post, I was having this issue intermittently for a long time, but your post led me in the right direction. The source of the error (Although really poorly documented and written) is covered here: Client Settings | Couchbase Docs (I am also using 3.0) but its the same.
" If lcb_get_bootstrap_status
is returning with LCB_ETIMEDOUT
and you are running on a slow network, modifying this setting may increase the chances of success."
I appended my connection string
couchbase://test.com/bucketName?config_total_timeout=25 and was able to fix it. Looks like its couchbase client failing to get connection config from server in time. You may have a connectivity issue reaching your couchbase server