Unfortunately according to one Googler Orrin, it seems that this isn’t an issue with the update itself, but rather a hardware issue, meaning that there’s nothing that Google can do from their end and users will have to take their phones in for repair or to be replaced if it is still under the warranty (this has since been confirmed by Google as well).
“We understand that a very small number of users are experiencing a bootloop issue on the Nexus 5X. We are continuing to investigate the situation, but can confirm that this is strictly a hardware related issue. For those of you that are currently experiencing this, please contact your place of purchase for warranty or repair options.”
The good news is that since the Nexus 5X was released in September 2015, this means that you guys should still be covered by the warranty so you’ll want to get this addressed ASAP. This isn’t the first time that updates have messed up devices. Just recently, Apple’s iOS 10 OTA update ended up bricking some handsets, although thankfully in this case a software fix rectified the problem.