my s8+ is certified according to the playstore.
if yours isn't, then do the wipe/cache magic.
instructions:
1) settings -> developer options: If you have OEM unlock set to "On" , then turn it off.
if your device is running oreo 8, then be careful with step 1! Oreo will reset to factory defaults if you confirm the OEM unlock = enable"
2) clear google play store data and cache;;
3) disable the app;
4) enable it again;
5) also wipe dalvik/cache.
with that said, my tab s3 (sm-t820) with oreo and non-rooted is showing as uncertified. My case is not unique. Accordjing to this article, samsung must answer.
Android is an open source operating system. That means that any company can take Android and modify it as they please to sell to their customers. Software experiences of Android devices can broadly differ, from that of the Google Pixel 2 to the Samsung Galaxy S9 to the Huawei P20 or the Xiaomi Mi Mix 2S. Google wants companies to take Android and customize it, but they also want to ensure that there’s at least some consistency between Android devices.
That’s why they created the Compatibility Definition Document (CDD), a list of requirements and guidelines that Android smartphone and tablet manufacturers must follow so their device can pass the Compatibility Test Suite (CTS). Passing the CTS is required if the company wants to be allowed to pre-install Google apps and services on their device. If a device doesn’t pass CTS, then they can’t ship a device with the Google Play Store or any other important Google apps pre-installed.
https://www.xda-developers.com/how-to-fix-device-not-certified-by-google-error/
