I found the solution myself. I deleted the *.ldb files in the Local Storage folder and the other devices are gone. You can find the folder here Opera\profile\data\Local Storage\leveldb\xxx.ldb

I have the same problem. I did a reset of my synced data but in the "opera://startpage/activity" I can still see all the old devices. How can I reset them?

I found the solution myself. I deleted the *.ldb files in the Local Storage folder and the other devices are gone. You can find the folder here Opera\profile\data\Local Storage\leveldb\xxx.ldb

I have the same problem. I did a reset of my synced data but in the "opera://startpage/activity" I can still see all the old devices. How can I reset them?

Unable to login on my iPhone to my opera account
opera version 16.0.12
iOS version 11.4.1

can you please solve the problem?
On my android and computer the sync together with the passphrase is working fine.

Please add this feature to your mobil browser. I need it. This is very important.