I would suggest you to take the drive out of the NAS device and run test on the drive using WD Drive Utilities in order to isolate the issue with the drive.
Refer the link provided below to test the drive using WD Drive Utilities.
“pending sectors” are not “bad sectors” - merely suspect ones - they can get that way for a large number of reasons (vibration, psu issues, etc)
You need to test the sectors in question to see of they get mapped out - and even if they are, that’s only 7 actual bad sectors out of at least 1500 available spares - I’ve had drives occasionally develop a few early in their lifespan and then put in 5-7 years more service without missing a beat.
Personally I would only worry about it if the drive started developing an increasing number of bad sectors (I had this happen recently on a WD20EFRX with “only” 38,000 hours on it. Mostly these drives last 50,000+ hours) and that slowly increasing number of bad sectors was a good warning to change it out before it failed. Bench testing after removal whilst erasing before disposal caused it to quickly go from 150 bad sectors to 1600 (it marked itself permanently failed as it crossed the 1450 reallocated sector threshold)