What's the soil like in the pot? Does that 'saucer' under the pot hold water?

No i never have water sitting in the saucer. The moisture meter I have always says the soil is moist but not wet however it can stay ’moist’ for up to two weeks.

That could be the problem. They're a semi-epiphytic plant, growing up trees with their roots on the tree trunk exposed to the air. Rain moistens them but they have good air movement. You'd be better off putting them into a light, airy soil , although you might have to water a bit more frequently. They'll be better off for it.

Something like you would use for an epiphytic orchid would be good. The main thing is to have a 'generous' amount of breathing holes around the roots. That's something that ordinary potting mix wouldn't give you.Just remember that in time the organic component of the mix will break down and the remaining soil will become compacted. That would be a good time for repotting again.

and, yes to the above. orchid bark (I use reptile bark) and perlite is good! add in with your potting mix.