Unresponsive in App, but fine via Alexa

I have a device that is unresponsive in the app - it’ll just say “turning on” or “turning off” for ages if I try to change the state but nothing ever happens.

But oddly, it responda instantly via Alexa. Ie if I say “Alexa, turn on the Rope Light” it instantly comes on. Same for off.

It’s a Fibaro Double Relay, so not officially supported. I’ve tried a few off the different communit device handlers but the behaviour is always the same.

I am using the Classic App. I haven’t dared to try the new one yet.

An pointers?