(Q): DS Save files deleting themselves over time?

hi all,
recently, I was playing my ds games on 3dsxl through the R4I Gold 3DS RTS,
and I have noticed something rather weird/strange with regards to ds game saves mostly (PSP/PS Vita/3DS/WII/GC/PS3/PS4/Switch saves don't do this),
not sure about GBA saves?

This issue mainly pleagues Ds games and I think, GBA games also?

I wonder why some ds games that should have data, (im positively sure they had save data),
don't, instead it's gone?

1) can save data for ds games or (for any game system)...

(Q): DS Save files deleting themselves over time?