And different ISP may has different lease time for assigned ip and the assiging of a new address cannot be guaranteed, you can stay the same ip.
it is always the same wallet.dat used and thereby everything runs synchronously
try it and you will see the result
I mean, while you wait for the next address to be assigned (which you can wait for a very long time depending on the provider), your second masternode does not work at this time. Accordingly, in these cases you do not receive a reward. I'm talking about lost profits / benefits.
Perhaps it depends on the coin. But, for example, those nodes that I keep do not allow downtime.
And if a restart is required (software update, power outage, etc.), then you have to perform the entire procedure again.