SA100 Volume control with app

I have a SA100 to play music mainly from the phone (spotify + 4stream) to a set of speakers in the house.
In the beginning (11/2021) I used to be able to control the volume from the spotify app.
After a little while (weeks?) and until now, the SA100 won’t react to the volume changes (+ or -) from the app. It only “acknowledges” them as I move the volume knob on the SA100. I mean with this that if I put the app volume at max, the SA100 onlty takes it over to max after I turn manually 1 step the volume knob.
I have sometimes been able to restore the control from the app a couple of times but it dissapears again and I don’t know how to restore it.
Is this normal? How can I regain full control of the volume from the app?
Is my unit defect?

PS: I found a thread about A50’s having too loud minimum volume. I tested and indeed I have something similar. Volume control from the app gives no response on the SA100, except when it comes to 0. Then the music indeed goes also to 0. The thing is that I am sure the output of the SA100 is certainly not too high because I can reach perfect control of the volume as I explained before when I use the manual volume knob of the SA100.

Thanks in advance,

FYI: SA100 is up to date (firmware 4.6.337862.28 of 20211206)