When I went to sync.opera.com to check for an Android tab that wasn't syncing, this is all I could get

It's the same with android version of Opera. There was no spinning circle like always. I tried clearing the cache and cookies along with disabling ALL of my extensions and STILL no luck.

I had to use Firefox in order to get to my data. And no, I did NOT reset my data. Here's proof that I'm able to get to my data in FF.

I thought it might be a chromium issue at first, but I was able to get to my data on Vivaldi as well as FF so I'm assuming that the devs must have been messing with something because I NEVER had any trouble with going to sync.opera.com before today either on pc or android. Opera has become the worst browser there is with so many issues that just keep piling up with each new update.

It's as leocg says. Once you reset sync, the data gets deleted from Opera's servers completely and is gone for good. The only way to recover the synced data is if you hadn't deleted any of your data from your pc/tablet. That means whatever history, bookmarks and passwords are the only data that'll get synced after the reset.

Try sync.opera.com. If you use sync any history older than 3 months should be there.

You're very welcome. Glad to have been of help.

You can try the FB Purity extension and see if that works.

You can try places like Aptoide or Apkpure. They always have older versions of android apps. However, be warned that you will have to uninstall your current version of Opera inorder to install the older one. That means that all of your online pages and history will be lost, but your bookmarks, speed dial, and passwords will still be available when you login to sync. This is the only way to do it on Android. If you decide to do this, I would also suggest you turn off auto app updates for the Google store otherwise, you'll just be upgraded again.

If it's avaiable for chrome, you can add it to Opera using this extension: Install Chrome Extensions. Also I see that it requires a desktop/pc version as well, make sure you have the program installed on your machine. That could be another reason why Chrome opened when you tried to add it.

It's really not Opera's fault. The Windows 10 issues might be because you have Windows 10 Creator's Update (build 1703 or above) installed. I had no problems with Opera on Windows 10 until the moron at the repair shop installed Creators Update on my laptop without asking me what was my original OS. So I'm stuck with it since I have no way of rolling back to good old Win 10 1607. Creators Update is the worst version of Windows that I've had. And I've been through plenty of them.

I think that's normal with sync. My most recent tabs are always replacing previously
opened tabs if I close them so I keep the ones I want to sync open when syncing. You can also try checking your history for those tabs at sync.opera.com as long as you don't have Opera clean the history when exiting.

@xmartincodes Try clearing your cache and cookies.