had some time in the weekend, and attempted to replicate the problem. but could not.   both client and server were able to reconnect without needing re-login after cutting off internet for more than half-hour.   tried to cut off at computer, or cut off at router, same.  
even when starting remotly without internet, it was able to re-login itself after internet is resumed. 
even closing and restarting without internet -- and pressing "cancel" and back to login screen -- it re-logs itself in once internet is resumed. 
it was also a fact a few days earlier that both client/server did require re-login.  not sure what the difference was.   
the only thing I could think of was that my router had problem then, and I was troubleshooting, internet was on and off again and again, also switching from cable to cellular network and back again and again.  maybe it confused remotly --  for example,  the login process itself was interrupted. 
anyway, maybe this turns out to be a false alert again.