Personnally, I am almost sure of the reverse as your description mentioned that you have change the name server and nothing else.

JMS Multisites just process the information it receives and if you provide it wrong one, the result would be to display the master website instead of a slave.
So for me, your description seem the describe a configuration problem in your server.
Why do you want to change something that was working when the new change you did is somewhere else. You have to investigate on where you change the thing to ensure be ok.

You just mentioned that the master is working but on plesk, each domain or subdomain has specific configuration.
If you want that I analyse more in detail your server configuration please order my billable support or contact the support of your hosting company that perhaps could help you in the configuration of your plesk.