Hi ​@NatsuEND !

From Deezer page Where Has My Music Gone on Deezer?

"Music I downloaded has disappeared from my device. Why?"−

If you've downloaded music to your device and can no longer play it, it is because your subscription has changed or expired.

You have to be on a Deezer Premium, Deezer Family, Deezer Duo or Deezer Student plan to download music. If you decide to unsubscribe from Deezer, your downloaded tracks will not be lost, but you will not be able to access them until you resubscribe. As long as you resubscribe with the same account, all your downloads will be there.

here is link

https://support.deezer.com/hc/en-gb/articles/115003846785-Where-Has-My-Music-Gone-on-Deezer

or contact Deezer support /Chat 

https://support.deezer.com/hc/en-gb/requests/new

I am a Deezer premium member.

Hi ​@NatsuEND ,

After downloading the songs or album, can you see the download icon when viewing your favourite songs?

Yes I can now I fixed the problem last night.