Earlier this week, Microsoft released Windows 10 Mobile Insider Preview build 14267 to the Fast ring. Despite only one known issue that was listed (which referred to Visual Voicemail), Lumia 550 users have reported an entirely different issue.
Some users are reporting that when placed on a charger, the Lumia 550 does not show that it's charging. The user who initially posted the problem stated that he was able to roll back to a prior build before the battery died.
In our own testing, we have found that our Microsoft Lumia 550 refuses to charge; it also is no longer recognized by the PC, leaving the Windows Device Recovery Tool off of the table to roll back.
Microsoft's Gabe Aul has been made aware of the issue, with users complaining that a hard reset fails if the power level is below 40%, and so far there isn't an official acknowledgement or workaround that we know of for anyone that has a drained battery.
At the moment, it seems like the only answer for those that can't roll back is to shut off the device, preserving as much power as possible, hoping that the next update fixes the issue. OTA updates for Windows 10 Mobile require at least 40% battery life, so it's best to not let the device fall below that.
As we know, these are the risks we take by signing up for the Fast ring. The best solution for now, of course, is to simply not install the build on a Microsoft Lumia 550.
We will continue to update this story as we find out more.