SASL AUTH failed on macOS High Sierra and Couchbase 5.0.0

When I create a bucket from the console (no bucket password), and try accessing it with cbc (from libcouchbase 2.8.3 or the one I built from the GitHub master), I get SASL AUTH failed:

$ cbc cat thisisatest -U [couchbase://127.0.0.1/mybucket] -v
0ms [I0] {9569/307} [INFO] (instance - L:423) Version=2.8.3, Changeset=8ce52f9294cfef59b9ff44f3cfc18cc3ca8c2860
0ms [I0] {9569/307} [INFO] (instance - L:424) Effective connection string: [couchbase://127.0.0.1/mybucket?console_log_level=2&]. Bucket=mybucket
7516ms [I0] {9569/307} [INFO] (instance - L:137) DNS SRV lookup failed: DNS/Hostname lookup failed. Ignore this if not relying on DNS SRV records
7516ms [I0] {9569/307} [INFO] (cccp - L:151) Requesting connection to node 127.0.0.1:11210 for CCCP configuration
7516ms [I0] {9569/307} [INFO] (connection - L:467) <127.0.0.1:11210> (SOCK=0x7fa8f5f00bc0) Starting. Timeout=2000000us
7517ms [I0] {9569/307} [INFO] (connection - L:141) <127.0.0.1:11210> (SOCK=0x7fa8f5f00bc0) Connected established
7517ms [I0] {9569/307} [ERROR] (negotiation - L:147) <127.0.0.1:11210> (CTX=0x7fa8f5c06d00,sasl,SASLREQ=0x7fa8f5c06ba0) Error: 0x2, SASL AUTH failed (ref: "546554a1-7e95-4ab1-6e3d-6a6003d57e6c")
7517ms [I0] {9569/307} [ERROR] (cccp - L:165) <NOHOST:NOPORT> (CTX=0x0,) Could not get configuration: LCB_AUTH_ERROR (0x02)
7517ms [I0] {9569/307} [INFO] (confmon - L:182) Provider 'CCCP' failed
7518ms [I0] {9569/307} [ERROR] (bootstrap - L:170) Failed to bootstrap client=0x7fa8f5c04b20. Error=LCB_AUTH_ERROR (0x02), Message=No more bootstrap providers remain
Failed to bootstrap instance. libcouchbase error: Authentication failed. You may have provided an invalid username/password combination (0x2)

I tried reinstalling from scratch, rebooting, several machines with the same software levels, the behavior is the same on all machines.

Any idea what's going on? Everything worked fine until I upgraded all versions to the latest.