Having had significant iOS app connection issues with my Pyronix Euro 46 alarm system, I reached out to Pyronix customer support. Although they are primarily geared up to discuss technical issues with alarm installers, they did help me via email (and also a phone call, which I missed).
Customer support supervisor Emma W. sent me a PDF manual, helped me to check my WiFi signal strength, considered the various app errors I was getting and finally suggested an alternative hard-wired connection module, might be needed.
Getting the alarm installer back in today resulted in an upgraded WiFi board with external aerial, and the signal strength now supports regular connection to the alarm's control app. They also enabled silent alarm setting so I don't disturb my wife (who always goes to bed earlier than me) when setting the door sensor alarms.
Overall, I am very pleased with the outcome, so thank you Emma, Pyronix [and also Invader Security].