InReach Explorer will Not Sync

I attempted this from a different computer, with the same result.  This would seem to me that this indicates something in the device is causeing the problem possibly.  I have done a soft-reset of the device (Pressing X and power button), and no change.

For the most part, you've done all the conventional wisdom steps.

You had a good cable originally if the f/w update worked. You have tried a different cable.

You have tried logging in and out.

You have tried different computers.

I only have a couple of suggestions.

First, make sure that you are logged into the correct account. Garmin Single Sign On (SSO) sometimes screws things up for people who have multiple Garmin accounts (for example, one for each device they own plus one for the forums). Be sure that you are logged in with the credentials for the proper device. (And no, being logged into the wrong account would not prevent the f/w update. In order to accommodate the update of devices that are not activated, the sync program will do f/w updates even when not logged in, or when logged into the "wrong" account.)

You might try clearing the browser cache. Or using a different browser (one that you don't typically use with Garmin accounts). This is not because a different browser is more likely to work better. It's another way of avoiding cookies, cached data, etc.

The sync program produces a log. You will find it here on a Windows PC:

"C:\ProgramData\Garmin\inReachSync\sync-log.txt"

It's not easy to read, but it is understandable enough that you might be able to discern the problem by looking at it. It's cumulative, so you want to look all the way at the end for most recent data. Dates and times are UTC, so time zone translation is required. You ought to be able to at least see your login account, as well as each time the device connects or disconnects.

You can also try a hard (full) reset followed by a sync. This will wipe all of user data off of the device. You will also have to repeat the outdoor portion of the activation. There is no real reason why this should help - but it's a last resort. And it MIGHT help.

If none of that pans out, you'll have to open a support ticket. They will probably want to see the sync log.

Just to add my two cents, I have the same issues (hardware 3.4 and firmware 4.2), I have followed the steps Twolpert recommended, and nothing

I have opened a support ticket...

I had a similar type of problem with Sync and my Explorer+ in October.  I finally determined that I could not access and download the latest version of the Sync program, which is 1.4.7.4776 (file name "inReach Sync en-US 474776.exe" for Windows).   So I temporarily installed a popular browser just to get the Sync I needed, and that fixed the 'hangs with "Determining Updates..." ' as well as other spurious issues.  HTH and let us know if this works for you.

It worked!

After doing all of the troubleshooting (updates, cables, etc.) I think I figured out a solution to the sync hang.  I'm on Win10 with the latest of everything as of this date.
It seems if you have "Settings->Tracking->Auto Track" On, the sync will hang.  I suspect the firmware in the Explorer+ is opening a file with some type of restricted access which blocks the inReach Sync from reading it.
I turned Auto Track off and the device sync'd right up.  Unfortunately, it "reduced" some of my tracks to the 10 min interval so I lost some data because of this problem.