Because they are not "real computers", there are known issues with mobile devices such as smart phones, tablets, i-pads and other such machines. Mostly it's a browser problem, but it could also be an operating system issue. Not a new problem, one that's been happening for years.
This is not just about Trad Gang either, because other forums and websites can, and are, having mobile device access issues.
SO ... if you are having access issues logging into Trad Gang (or other forums and websites) using a mobile device, but no problem with a real computer access, contact the mobile device manufacturer for possible assistance.