Kind of odd that they'd be experiencing issues NOW, but weren't before, the only thing I can think of is if someone had modified how something worked (or adjusted a design); not really much we can troubleshoot however, since the v7.5 tree isn't really optimized for mobile use at all.
v7.6.0 (so here, UBBDev, and a handful of other places [A Gardeners Forum, UGN Security, select beta testers who're alpha testing]) should be fully mobile capable as a stock archive; but some sites "designs" are going to make their site not mobile at all (just how the designs for their sites that are integrated on their forums will affect the viewing ability, by just making the page too wide).
