How to Fix: Power Options say No Sleep (Battery or Plugged In) but it still sleeps

Brand new Inspiron 17 7786, Win 10 64 bit Pro.

Power options are explicit, but long network copy is failing because the Inspiron goes to sleep while receiving data!

a) Anyone know why?

b) Anyone know the fix?

NB It also doesn't stay awake even when I am using Insomnia (see https://dlaa.me/blog/search?query=insomnia), which works perfectly well on the Win 10 (64 bit Home) desktop

Thanks!

Julian