Hmm for me, and I think for most users too, it can't be Apple core functions aka System Services because these aren't shown in the Status Bar (because 99% of time one of them would be always on).I think it is a number of Apple core functions that are doing this. For me it was WiFi Networking. For others it is Weather. For others still something else. It cycles from solid purple to outline to solid to ... Does it eat battery? Don't know yet. I do know I am okay with 11 on my iPad Pro 12 v2. Not happy so far on my Mini 4 and 7+.
Will see how it goes.
btw - The location issue was apparent on all my devices. All had the same issues.
And yes, I think my iPhone 7 is draining faster than usual. Just annoying.