chnb, I have search on google like crazy but I am unable to find anything related to elmulex/elxnet 11.4.1255 or 11.2.1271.
Can you provide a deep link to a release note or download page?
We've seen something similar on the HP 556FLR Emulex adapter. The latest driver HP has published is 11.4.1205....
HPE has published this advisory:
Advisory: VMware - HPE ProLiant Server Configured With Certain Network Adapters And Running VMware ESXi 6.0 U3 May Randomly Lose Connection to Individual Virtual Machines
We have installed the driver released by vmware (11.2.1271) with good results. We have 1,5Weeks of stable operations and counting.
It may look like it's an older version than the one released by HP but apparently, according to HP support, they use different numbering (although the same basic format).
We have now upgraded all our hosts to the latest HP SPP (2018.03.0.B) and the latest vmware release and latest HP drivers (apart from the Vmware supplied ELXNET driver). All our blades are BL460c Gen9 with 650FLB adapters and we run virtual connect 4.62. Hopefully this means we will have stable operations during summer, but you never know