Roon android app does not find core

[BlackJack]

Detection sometimes needs a loooong time. If your impatient, this trick might help (I used it myself already with success):

Android can't find Roon Core

For the umpteenth time my Android phone would not connect, so I went into help and instead of of putting the IP address of my Core I put 255.255.255.255 and it found it immediately.