Wd elements 5 tb pochet disc

Hello

My wd elements hard disc pocket 5 tb is up to 600 gb free space (85 %)but suddenly only files named A to O are visible on search index
I checked by adding an extra file called Toad ( big as 750 mb)and it was vissible added but in 1 second it vanished and cant be found anymore but the volume increased with 750 mb so its still on the disc but not to be found on the index
Added twice with same results !
Guess the content list / root is corrupted ?
Any suggestions how to refind the P to z files ( big 1.5 Tb) on my disc ??
They are in a kinda twilight zone ?
I.m kinda nerd in this so please keep suggestions kinda simple for me
Thanx already
Jan Horjus

Your WD Elements 5TB drive may have a corrupted file system, causing files to disappear while still taking up space. First, check Disk Management to see if the drive shows errors or is marked as RAW. Try running CHKDSK by opening Command Prompt (Admin) and typing chkdsk X: /f (replace X with your drive letter). If that doesn’t work, use data recovery software like Stellar Data Recovery, Recuva, Recoverit to scan for missing files. Also, connect the drive to another PC to check if the files appear. If recovery software finds your files, save them to another drive before attempting repairs.
https://www.stellarinfo.com/blog/external-hard-drive-data-recovery/