Yep,
Which makes little sense,
/R and /B imply /F.
/R and /B are somehow contrasting options.
/R scans areas NOT marked as bad (i.e. not listed in $BadClus) and sees if there is anything to be added to the list.
/B scan all volume and "judges" whether areas already marked as bad can be "promoted" to good and adds any bad area to the list.
If you prefer, /R trusts the existing info in $Badclus, whilst /B ignores it and represents a sort of "second opinion".
Still on modern media, any bad (or even "weak") sector should normally be detected by the controller and remapped to a good spare sector well before and besides any chkdisk activity.
Get a tool that can read the S.M.A.R.T data, example[1]:
https://hddscan.com/
look for items #5. 187, 188, 197 and 198:
https://www.backblaze.com/blog/what-smart-stats-indicate-hard-drive-failures/
and post what you get on that disk.
Post the exact make/model of the disk, usually there are manufacturer tool that can do deeper analysis of the device.
jaclaz
[1] there is a much more compact and nifty as usual tool by Nirsoft , but it doesn't show the SMART parameter numbers;
https://www.nirsoft.net/utils/disk_smart_view.html