Php client errors


I am getting multiple errors of this type:
[cb,WARN] (lcbio_mgr L:463 I:1387430426) REDACTED:8093 (HE=0x563b0bd8c650) Pooled socket is dead. Continuing to next one’
Also there are other errors happening in the same time, not sure they are related:

[cb,WARN] (lcbio L:109 I:3297726731) Translating errno=111, lcb=0x400 to NETWORK_ERRORPHP message: [cb,EROR] (connection L:164 I:3297726731) REDACTED-SERVER-01:8093 (SOCK=6d405a84bb57b3e3) Failed to establish connection: LCB_ERR_NETWORK (1048), os errno=111PHP message: [cb,EROR] (http-io L:218 I:3297726731) Connection to failed with Err=0x418PHP message: [cb,WARN] (server L:382 I:945053762) REDACTED-SERVER-02:11210 (CTX=0x563b0bccadf0,memcached,SRV=0x563b0bc76ba0,IX=2) Received server error LOCKED (0x9) on packet: OP=0x94, RC=0x9, SEQ=117’

Most of the queries are working, but from time to time, I get the above errors. I don;t see any other errors in the Couchbase cluster, and Google searching doesn’t bring any results.

What could be the problem?