Your issue is very strange.
How can a physical switch change the default gateway?
Your network is correct and default gateway is in the right network?
Have your tried to add using CLI with route command?
Yes, That is how I get it back on the network.
Discovered changing the IP via the esxcfg-vswif command did not clear references to the old network out of the vswif configuration file. In each server that had a problem, there was a line "NETWORK=old network IP". I removed the line and the problem stopped.