What issues are you having signing in on mobile skin? There is a "hamburger" menu at top left, click that and click LOG IN.
This morning, for the first time, I managed to login. I was not able to do so until some of the adverts had loaded.This took nearly 15 minutes. When I got to the log in page the blessed floating header kept getting in the way. It took me another ten minutes to manipulate the header out of the way of the user name and password boxes. Once logged in the header kept getting in the way and I had to log out or go mad. I logged out.
I usually only go onto the internet with my laptop a couple of times a week. In the past I have been able to view the site on my handy without problems. From now on i will have to limit the amount of time I spend on Pprune.