Let’s say I have a double bar and a change of tempo and I place a metric equivalency marking of (e.g.) quarter = dotted eight then add the new metronome mark then the metric mod disappears. I’ve found a workaround by putting the metric mod symbol at the previous barline then drag it over to where I want it, but is that supposed to happen?
You can only have one tempo item at the same rhythmic position, so yes, this is the expected behaviour at the moment.
Hopefully a change will come.