I use an android 9.7" tablet and an android Nokia 1 Plus phone as devices during app development.  This means running the B4A Bridge.  Never a problem on the tablet, but on the phone I get the warning message "Please enable installation of non-market applications.  Under Settings - Security - Unknown sources, or, Settings - Applications - Unknown sources."  I have changed the appropriate settings but still get the message.  It does not stop me, I can just press 'OK' and continue to use the B4A Bridge.  It has only started showing the warning since the last upgrade to android 9.  Has anyone a similar experience?  My phone supplier can't bottom it.