My C5 used to connect last year to my Iphone 8+, but after many updates from Apple. It no longer wants to connect. I'm running IOS 12.3. How ever I got it to work by by going into the Iphone's wifi and setting the Configure IP to manual.
If you have problems with Android, maybe this workaround will fix it too?
I don't have an Android Phone.
Another workaround is to place the Iphone in Airplane mode. My work around allows me to Join/connect the C5 when ever I want to.
Here's what you do.
#1 Go to Wifi settings, and connect to your C5
#2 Click on the I
#3 Click on Configure IP and change from automatic to manual
#4 Disable Auto-Join
#5 Set IP Address to 192.168.1.2
#6 Set subnet mask to 255.255.255.0
#7 Set router to 192.168.1.254
#8 Now run the C5 app, and it now works.