If someone get hidden.img error when flash stock rom:
DON'T PANIC like me

Even if you reboot your device you see something like corrupted update firmware bla bla bla.
1. DON'T PANIC!
2. Rename home_csc file - erase .md5 at the end,
3. Using winrar you must unpack home_csc file,
4. find hidden.img, copy it to your favourite plac on computer like: C:/ files/photos of vacation/secret/porn or where you like
5. at the end of name "hidden.img" add .tar - it must look "hidden.img.tar"
6. reset phone to download mode - you must press seven seconds vol down + bixby + power buttons - next of course vol up to continue
7. In ODIN add only hidden.img.tar in CSC file
8. Start
9. after finish phone normally boot.
10. Next steps like in instructions like skip every option, do factory reset etc
I've got this problem in polish version of SM-G955F branding in PLUS GSM, but i think i'm not only one. Maybe add this instruction to first post