I wish Google would actually ship an OTA update that fixes blueborne for Nexus 5X... Not sure why they haven't done it.
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I gave up waiting. But it turns out that manually applying the downloadable OTA updates with adb sideload is pretty straightforward.
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I think developers.google.com/androi… was my source, but can double check. I found getting into fastboot by using buttons to be easier.

Oct 3, 2017 · 6:55 PM UTC

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And I did apply the updates in sequence, though not sure if that was necessary.
Replying to @davidbaron
Thanks! I'll take a look!
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