“A general system error occurred: Failed to start migration pre-copy. Error 0xbad003f. Connection closed by remote host, possibly due to timeout.”
“A general system error occurred: Failed to start migration pre-copy. Error 0xbad004b. Connection reset by peer.”

Another issue, that I recently came across was a live vMotion issue where the vMotion migration would fail during the pre-copy and always at 10%. The following issues were either one of the two:

I performed some basic troubleshooting such as a vmkping. I used the ping command and watched the response times remain consistent during the attempted vMotion migration. No packets were being lost which I thought that there would be packet loss if there was an issue with Layer 3 IP addressing.

While still on the command line with the ESXi host, I decided to look for any arp entries anyways regardless of my logic to rule it out. I ran the following:

cat /var/log/vmkernel | grep arp

I was wrong, there was another host on the network that had the same IP address!

I found a new IP address for my VMKernel, updated DNS then updated the IP address on the ESXi host and my issue was resolved!