[ecksmc]

Over Christmas I noticed that a device I had been using wasn't showing up when I opened Android device manager app this was a little alarming, after doing a lot of things like clearing cache and data from several of Google's apps like ADM(android device manager),play store, frameworks etc... I still wasn't seeing all my devices even online at google store-devices I was only see 1 device, I do like to find solutions myself but I was beat here after a search and reading loads of articles I finally found a solution, I had done the right thing by clearing cache and deleting data from some apps but it seemed that you have to do this in a particular order and you need to keep to this order, skipping any part is just going to be a waste of time, after I done this in order all my devices were showing again, yes I had to this with every device which wasn't showing on play store in devices or in the ADM app.
So here is the fix

From Ryan Lestage on Google+:

Clear data for the following apps:

Play Store
Download Manager
Google Services Framework
Restart your phone.

Fire up the Play Store app.
Wait for the device to show again on the web Play Store. It will appear under Settings > Devices. It may take a half-hour to several hours to appear.
When your phone has shown up in the Play Store with the date registered as today's date, proceed with the next steps, but not before.

Open Google Settings from your device's apps menu.
Touch Android Device Manage(security).
Uncheck Allow remote factory reset.
Go to your device's main Settings menu, then touch Apps > All > Google Play services.
Touch Clear Data. Note that this action doesn't remove personal data.
Go back to Google Settings and Security and select Allow remote factory reset.
Restart your device.

Just remember do this in order, also only do this on devices which are not showing in ADM app and wait till you see device on web at play store devices before completing stick to the order.

[elMika70]

Thanks, this fixed the issue with my LG!

[Leapoffaaaith]

Thank you Thank you Thank you! I was about to reset the entire phone. You saved me hours of effort, Please pass on my thanks to your source.

Fixed Lg G4 running stock

Follow every step or start over!

[nicetucu]

What I did was to clear cache with application manager with google services and google play (not even sure you have to do this). Open your chrome browser on your phone and go to the play store and sign in.

Go back to the play store on your computer and should see your device again.
It was working fine for almost two years and perhaps through an update, it needed further authentification.

[Gagan Sembhi]

This worked for me.
Thanks for contacting Google Support.

You can manually prompt an account sync by doing the following:

Go to Settings.
Under the "Accounts" section, touch Google.
Touch the Menu icon (three vertical boxes) on the top right, then touch Sync now.
If this doesn't work initially, you can go through these steps to force a successful sync. You may also try manually syncing again between each of these steps, to verify whether they've worked.

Step 1: Verify your data connection.

Open a browser on your device and attempt to navigate to a website (such as news.google.com).

If the page doesn't load, the sync issue may be occurring because your device simply can't connect to the internet at all. If so, just reply to this email, and we can try troubleshooting your device's connectivity.

Step 2: Force an account sync using the date settings.

Navigate to Settings.
Scroll down to System and touch Date & time.
If the phone has the following options, uncheck them:
Automatic Time Zone
Automatic Time Updates
Manually change the date and time, so that they are incorrect.
Touch the Home Screen button.
Go back to the Date & time settings.
Manually change the date and time, so that they are correct.
Re-check the boxes for Automatic Time Zone and Automatic Time Updates
Step 3 (Phones Only): Force an account sync using the dialer app.

Open the dialer app.
Touch the keypad icon.
Dial *#*# checkin #*#* (literally: *#*#2432546*#*#)
Touch the green phone icon.
If successful, an alert notification will appear in the notification bar a few seconds later. This notification will say whether the phone was able to check in.

Step 4: Clear Storage cache and clear "Contacts storage" data.

If you have saved new contacts since the last time you were able to sync their phones, you can back up their contacts before clearing your contacts storage.

Open the Contacts app.
Touch the Menu icon (three vertical boxes).
Touch Import/Export.
Touch Export to save the current contact list.
Touch OK.
Later, to restore the contacts from storage, go back to the Contacts app and touch Import/Export > Import from storage > OK.
After backing up contacts, proceed with clearing the contacts storage and cache.

Go to Settings.
Under the "Device" section, touch Storage.
Touch Cached data, then touch OK to confirm.
Go back to Settings, and, under the "Device" section, touch Apps.
Swipe from right to left to get to the "All" app section.
Scroll down and touch Contacts Storage.
Touch Clear data, then touch OK to confirm.
Step 5: Uncheck "Sound Search for Google Play."
Go to Settings
Under the "Accounts" section, touch Google.
Touch the Gmail/Google account that's experiencing the sync error.
Uncheck the box for Sound Search for Google Play.
"Sound Search for Google Play" may not be on the list. If it's not, skip to the next step.
Touch the Menu icon (three vertical boxes) on the top right, then touch Sync now.
Step 6: Remove and re-add Google account.

You may need to remove the account, and add it again. To do so, follow the instructions on this page.

Step 7: Try to log in from other places and try to sync again later.

If possible, try syncing from a different location or Wi-Fi network. It may also be possible that there is a temporary issue with the account sync services, and you should try syncing again later.

Regards,

Google Support Team