Offline songs don't play when network is not available

[bengogo]

Hi,

I have been using Spotify with premium for about 2 years now.

I was happy with the service until lately when I started to have an interrupted network moving in and out the subway (usual situation in a city). So here it is, I am aware that the song I did not save into my device should not keep playing, this happens so that s ok. My issue is about the songs I have saved into my device, I spend a lot of time trying to maintain an offline playlist suitable so when i don't have network i can still enjoy music.
My question is: why songs previously saved (with icons ticked) aren't playing clearly/at all and I must keep press forward button to find one song working? Also the app is really slow to update screens and move from views to views - probably doing api calls which aren't responding (not my issue as I have offline songs right?..)
I find this so frustrating that i feel like interrupting my premium account, I use to have all my tunes available via mp3s and now I feel like going back to my previous set up to enjoy my music offline again.

my device is a Samsung S7 with Android 7.0

thanks,

Benoit