What model was it? Most manufacturers only test their hardware on Windows. Canonical maintains a list of devices that are certified to work with Ubuntu[1].
Be careful about trusting that certification. Note that the 3rd gen Thinkpad x1 Yoga[0] is "certified," however, there is a critical change in the BIOS that prevents the laptop from using s3 sleep mode, apparently to switch to some proprietary Windows sleep mode. Therefore, without any changes, when you close the lid, your battery will drain at about the same speed as if the laptop was running. This is obviously untenable.
The solution is to manually patch your BIOS, which doesn't always work and is extremely technical. It's also not a solution provided by Lenovo, so officially, there is no solution.
Ninjaedit: Hmm, it appears Lenovo may have finally issued a BIOS update to fix this issue.
I think the certification means, that all the hardware parts of the device are supported by the OS. The device itself might not even be tested to see if there are no other issues. Generally, it's a problem with newly released devices, that don't have many active users yet.
[1] https://certification.ubuntu.com/desktop/