Ringtone keeps changing back to the original default tone (over the horizon)

[Members_NmfiOtj]

i have installed a mp3 file on the phone and moved it to the ringtone folder (internal)  and it works for a day or so then it reverts back original default tone. 

I have done the fowlling:

-Reset the phone (no help at all, I have even tried it on a formated phone(s20 5G)the same issue)

-Change back from darkmode to daymode (some forums say ti would work)

-moved the file to SD-card  and back 

any thoughts? 

[BandOfBrothers]

I wonder if the file is in some way not compatible,  corrupted etc.

If you change ringtone to another pre downloaded option does that stay chosen?

I use zedge.com which has tones in the correct file format and have worked fine for me.

It's a free service.

Perhaps give it a try and see what happens @Members_NmfiOtj 

[Kokosmin]

I have this problem also, for many months now. At the beginning, with the same mp3 there was no problem keeping the same sound for ringing on SIM1. Always changes to default Quantum Bell. SIM2 is ok though, keeps its own custom mp3 ringtone.
S20 FE 5G with the latest updates. Even today, after the last update

I tried setting a ringtone from the phone's default list, but this is not working either.