Win PC reports problem with drive when connecting 520

It happens when you unplug the EDGE 520 from your PC before disconnecting the USB port.
Despite it is not advertised (or at least not mentioned in the User Manual) i recommend to analyse/defragment regularly the EDGE 520 drive (as all other Garmin devices that you can connect to USB). Especially on Edge 520, where you can save a lot of activities/ workouts as Fit Files and play with maps and segments.
I also did that regularly with my Fenix3 and VAHR (after a PC backup and suppress of the activity files on the Garmin drive).
I don't know if it improves a lot the read/write access time of the drive, if any, but at least it always solves "problem with the drive". And you can check that the Garmin drive is very often highly fragmented using Drive Analysis before.

With this method no need to do a hard or factory reset that will erase all your settings. Just defragment in [Garmin ] drive: / Properties

Thanks for the reply.
I have tried checking the drive and it says there are errors and give me the option to fix them.
However it then sits for a long time with a "Scanning and repairing...." dialog up.
There is a progress bar but its blank.
Is this normal behaviour and how long could it take?

In windows Explorer just go to
[Garmin] ("Drive:") / Right Clic / Properties / Tools / Defragment
then You choose again [Garmin] ("Drive:").
you can first do "Disk analyse" ; it will give you the % of defragmentation. second you do "Disk Defragmentation".

Depending of % of defragmentation and amount of used memory to defragment (used vs free Capacity in Mb) it will take approx 1-2 minutes? So not an immediate result.

Defragmenting Flash Drive storage is completely pointless. Flash Storage does not have a concept of 'linear read', data is stored in sectors of a specific size.
DO NOT perform defragmentation, as all it can do it make things worse.

flash drives should not be defragmented : in theory it it said that it does not increase access speed and might shorten the life of the drive. In practice I have never seen any positive/ negative impact doing this once every month or every 2 months on my Garmin watches.
However it always solved the issue when I got the "problem with the drive" message especially with the Edge 520. For this case I would be pleased to hear another solution than a factory reset!

My solution is to ignore the warning from Windows and not to reapir/defrag. My 520 has been doing this for 18 months plus. I've not seen any issues with updates or with corrupt ride files in that time so I just leave it alone.

I too had the disk error msg with Win10 since I purchased the 520 in June. I "repaired" it yesterday and no issues, took about 5 seconds, warning went away. Defrag disabled for the Garmin drive so not even an option for me.