Couchbase - Connection attempt failed if multiple independent connections start in the same time

I have another strange situation and I don;t know how to debug it.
It seems that if I start (fork) multiple PHP processess (50-100) - each one connecting to the Couchbase DB to get 2 documents, after a few seconds (1-3) I get multiple error with the message:

[cb,EROR] (server L:925 I:3176723080) NOHOST:NOPORT (CTX=(nil),SRV=0x55e30f4d1d80,IX=0) Connection attempt failed. Received LCB_ERR_NETWORK (1048) from libcouchbase, received 0 from operating system
[cb,EROR] (connection L:164 I:3176723080) readacted-sv-hostname:11210 (SOCK=98e75cd0e0cc38b0) Failed to establish connection: LCB_ERR_NETWORK (1048), os errno=99

In the same time, the CB servers load is less than 5%, the network is used less than 10%
Also, in the same time another server can connect to the DB without any issue.

After a few seconds and a few thousands of error logs things come back to normal for a few seconds, and then this repeats.
This happen on two independend servers at random times.

The only predictable thing is that this happen when there are multiple independent connections forked with exec(‘php script.php’);

Is there some kind of a buffer which can fill-up in the couchbaselib? Is there any setting I can configure for this?