We are on Sitecore 10.1 and after yesterdays deployment with only minor changes this warning flooded our logs on the CD servers: Can't check device type - device detection is not ready.
We did apply Sitecore's latest security patch KB1002925, where you are advised to delete the Sitecore.MVC.DeviceSimulator.dll and disable Sitecore.MVC.DeviceSimulator.config. But even after reinstating those two files the warning keeps coming. What is wrong?
Check that Sitecore instances can access this database path.
<setting name="DeviceDetection.DatabasePath" value="/App_Data/DeviceDetection" />
and Also validate whether device detection is enabled or not in this config App_config/sitecore/DeviceDetection.Client/Sitecore.CES.DeviceDetection.config. and https://www.yoursite.com/sitecore/admin/showconfig.aspx to check value.
It allows to download database. And also validate FailDatabaseCheckInterval.
<setting name="DeviceDetection.FailDatabaseCheckInterval" value="00:10:00"/>
You need to also check firewall settings and must open the HTTPS protocol on your firewall, either for the wildcard domain address *.cloud.sitecore.net (if your firewall allows it), or for the following URLs:
discovery-ces.cloud.sitecore.net
devicedetection-ces.cloud.sitecore.net
Here is the doc you can refer for device detection-related configuration. https://doc.sitecore.com/xp/en/developers/81/sitecore-experience-platform/configure-sitecore-device-detection.html
So as it turns out it didn't have anything to do with those two files. It might be the reason it started in the first place, but the problem came from a corrupted device detection database.
We had to delete all files under /App_Data/DeviceDetection/ and restart the Sitecore Instance.
