I am not aware of such issue with 7.5. I just checked and my iOS remote app seems to work fine, discovered the 4200 and 3100 device i have on 7.5.
The general support email is developer (at) roku.com but beware they are not very responsive.
If you let me know what your app is (PM if need be), i can try it locally. I try to keep abreast of any potential bugs and who knows, maybe 7.5 tightened something in security that i want to know. Try collecting more info from your users, like Roku and mobile IP, as well as Roku and mobile device version.