Correctly setup you wireless network and ensure you are running all the latest firmware/software.
Link: https://support.presonus.com/hc/en-us/articles/360028808611-Wirelessly-Controlling-a-PreSonus-StudioLive-Series-III-Mixer
Jul 2019 Updates.
Software Version Information:
Universal Control (Mac/PC) - v3.1.0.53214
UC Surface (iOS/Android) - v3.1.0.53214
QMix-UC (iOS/Android) - v3.0.0.51525
Hardware Version Information:
Series III — v2.1.16232
NSB 16.8 – v1.1.0.15533
NSB 8.8 – v1.1.0.15534
EarMix – v1.1.0.15533
SW5E – v1.0.0.15447
Supported OS Versions:
OS X 10.11.6 (El Capitan) or later
Windows 7 (x64) Service Pack 1 + Platform Update, Windows 8.1 (x64), Windows 10 (x64)
Android 5.1.1 Lollipop or later
iOS 10 or later