To schedule chkdsk for the next restart, the drive to be checked must be locked by, for instance, setting a command prompt's current drive to the same drive.

Opening files on the drive is not sufficient. Also, the /x switch must not be given.

C:\Windows\system21>d:
D:\>chkdsk d: /f /r
The type of the file system is NTFS.
Cannot lock current drive.
Chkdsk cannot run because the volume is in use by another
process. Chkdsk may run if this volume is dismounted first.
ALL OPENED FILE HANDLES TO THIS VOLUME WOULD THEN BE INVALID.
Would you like to force a dismount on this volume? (Y/N) N
Chkdsk cannot run because the volume is in use by another
process. Would you like to schedule this volume to be
checked the next time the system restarts? (Y/N) Y
This volume will be checked the next time the system restarts.
D:\>

If scheduling a check on the sytem drive and other drive(s) simultaneously, request the check on the system drive last, so that the check(s) on the other drive(s) are carried out only once.

Ref: https://serverfault.com/a/798951