We saw this issue last night (assumed by matching vmkernel logs), on a Cisco B200 M5 running ESXi 6.7U3 - UCS package and running version: 4.1(2a), with VIC 1340 adapter running version: 4.4(2d). Took down 39 VMs, unfortunately. Will raise a support case.
Also, I couldn't find anything on the open caveats on: https://www.cisco.com/c/en/us/td/docs/unified_computing/ucs/release/notes/CiscoUCSManager-RN-4-1.html
