Is there a known issue with Garmin Express requestcache.db being over 600GB

I'm almost 100% sure you can delete that 600GB file without any oblems.

I did a test with a spare PC that already had Garmin Express (GE) installed, but some version earlier than current.  I first allowed Garmin Express to do the update to the current version.  That went trouble free.  As always I then went into the Garmin settings and disabled the option "Always keep Garmin Express running in the background".  I then exited the program, went to the path you've mentioned and deleted the file named requestcache.db which was 64 KB in size.  I then restarted GE, exited, and reexamined for the presence of the file.  As anticipated GE recreated it, and it now was 16 KB.  So again I suggest you delete the file.  You can bypass the Recycle Bin it by clicking on the file in File Explorer, then hold down the Shift key while you hit the Delete key.  That should immediately free up the space for any security updates needed.  Then carefully observe the requestcache.db for size and check it occasionally to see if it starts to grow at a rapid rate.  

It is safe to delete this file as Garmin Express will create a new one when needed.

However if the new file continues to grow that large, please contact Product Support in your regions so we may gather all the information necessary to research this further.

What is it and what is the bug that let Garmin Express make a .db file that big?

The bug is also causing issues on other parts of the machine with that massive file (average computer would take a few days to compress it).

Why does it matter what it is?  I've told you it can be deleted, even did a test with my own GE to test that and indeed GE recreated the file.  EXPRESSCUSTOMERCARE also provided essentially the same answer.  In light of the fact that many thousands of people use GE without this issue, it would be very difficult to consider it a bug of GE.  Perhaps some pecularity with your Windows installation.  So just delete the file, and then should it begin to increase dramatically in size again, then as advised report the problem to Product Support.

It matters as it is a nasty bug and until there is a fix people need to know what kind of work around they can do.  If you have a fleet of machines and they all have that same bug do you want to go around to 30+ machine and manually delete that file (that can't be deleted with Garmin Express open)?

Google your problem, you are really the only person that has reported this issue.  Google ["Garmin Express" requestcache.db] and you get six hits, SIX!.  Two of which are yours and mine.  The quotes around Garmin Express by the way tells Google to search for Garmin Express and only Garmin Express.  Some like Garmin shipped by Federal Express will be ignored. 

People don't need a work around because the problem is something that only you seem to have encountered.  Delete the file and move on?  If it happens again then the appropriate people (EXPRESSCUSTOMERCARE) have told you what to do.

I never said it was mine in my first post.   Google must have index it based on the tags, others may not have noticed the bug yet (also seems to happen just on Windows and when using one of the Garmin Watches (not seen to many in the wild).

People do need a work around if the bug creates a security issue on the machine and also stability issues on the machine.  Just syncing and updating a Garmin Watch should not create a .db (database file) of over 600GB.  Need Garmin to fix the strange bug.

There are plenty of Garmin watches "in the wild".  From a reliable online business resource "We estimate Garmin shipped 1.5 million units worldwide in Q2 2021, rising a modest 25 percent from 1.2 million in Q2 2020."  NOTE, that is in one quarter of 2021! 

4340988 said:

others may not have noticed the bug yet (also seems to happen just on Windows and when using one of the Garmin Watches (not seen to many in the wild).

What is the .db for?

Windows takes over 26 hours to compress it (to under 20 KB)