Don't know if his helps, but "everything is up to date, latest versions" might be a problem. This is the "latest and greatest" for the legacy boards:
Universal Control 1.7.4 (v5773)
Universal Control 1.7.4 includes drivers and control panels for the following products:
* StudioLive 24.4.2 (Launch Window, Virtual StudioLive, Driver)
StudioLive firmware and build information:
* 24.4.2: Firmware Version 1.0, build 195
Driver Version: 4.2.1.46437
Universal Control Build:
* Mac/PC: 5773
Current App versions compatible with this Universal Control release:
* SL Remote 1.5 for iPad
* QMix 1.3 for iPhone and iPod Touch
It is important to use matching firmware and software versions. Here is the link to the download page of SL 24.4.2: http://www.presonus.com/products/StudioLive-24.4.2/downloads. There are problems reported with the latest iOS for iPhones, so it also might be worth to contact PreSonus' support.