Why does the LL 40GBASE-KR4 IP Core intermittently fail Auto-Negotiation and thus fails to link up?

Description

Due to a problem with the Low Latency 40GBASE-KR4 IP core, link training will fail, rx_pcs_ready will not be asserted, and register 0xB1 will return the value of 0x100.  This indicates that the IP core is stuck in Auto-Negotiation mode.
 
The problem is in hardware only and does not exhibit in simulation.  This is a start-up only problem, if rx_pcs_ready asserts the IP Core will continue to work correctly. 

Resolution

The problem is fixed beginning with the Quartus® Prime software version 16.0 update 1.