this issue was fixed in 11.3-U4.1

This has been attached. 

Also, everything is NOW finally synced and running again. But I had to reboot the server numerous times before it completed, as once the max pipe exceeded condition develops, most everything quits working (SMB, etc) until a reboot.  The internal default for 'kern.ipc.maxpipekva' is, I think, something like 10000. Prior to massively increasing this max value in Tunables, the error condition would appear after only about 30 minutes or so. Setting it to 256MB got me to about 2 days before I would have to reboot. Were this not an issue, I think my replication backlogs would've been all caught up in 48-72 hrs (if not sooner) as most snapshots are very small to zero byte in size.

Others on the forum had suggested more snapshots than could be pushed out, and, over WAN, I suppose this might prove true. But this is all over gigabit LAN. and, replication is automatic, so at any given snapshot(s) event interval, the number and size of snapshots to be replicated is really quite manageable. But should some replication setup not be, I would hope the GUI would be able to advise the user of this. But I really don't think running out of pipes should even be a factor here. I even tried disabling all but one replication task, and it still eventually errored out.

Anyways, thanks again very much for taking a deeper look into this! It really surprised me that simply just catching back up would prove such an effort. 

Thank you for the report .  Can you please provide a debug by navigating to System -> Advanced, click save debug, and upload attachment to this ticket?