To reproduce the issue:
- Go to Unity Preferences -> External Tools and delete Android SDK path
- Go to Build Settings and choose Android platform
- Notice that no run devices are displayed and console is spammed with error messages (might need to hit Refresh button if doesn't reproduce correctly)
Run Device section should show some message informing that Android SDK is unavailable or ask user to select SDK path.
Also I think that AndroidSDKTools.GetTools() should only be callable from UI thread only because it might ask user to specify SDK path. When it gets called from worker threads bugs like this happen. This might require reworking IDeploymentTargetsExtension and some other places.