Hello,
in fact I used SRTM 1Sec HGT .
1- I used my old DEMs.
2- deleted the old once and let SNAP download automatically
3- I downloaded DEMs manually.
But didn;t works
Finally I decided to uninstall SNAP and re-install it again but with the first choice of DELETING old user data.
and SNAP8 look it works good.
Many thanks for you ABraun and all SNAP team.