lets say  you do a sub net.

your main router is say  192.168.0.1-256

add a cheap  router  that is 192.168.1.1-256

so modem >>>> main router >>>>> cheap subnet router >>>>> attach 1 bad miner attach 1 pc  search with advanced ip or angry ip   see if it shows.

I had issues with early model s-9's  sound like this issue.

So  2 dead psu's
and 3 weird ip's out of 20 units correct?

To late now but the s15's in your case should have  been m10's

My 4 m10's = flawless  they do 59-60 watts  a th at  low setting about 20.5th

are you usa based?