My phone is a Nexus 5X. All I know is that the old Snapchat app would occasionally soft-brick my camera such that no other application (including the camera app) could use it until I rebooted my phone. I confirmed with multiple experiments that Snapchat was the culprit. After the redesign, the problem went away.

I recall that in Android if an app doesn't release control of the camera then no other app can access it until the phone is rebooted. I suspect this is what was happening here. AFAIK, it isn't a bug with the phone hardware etc. just poor os design. Hopefully they'll fix it one day.

Ref: 'Release the Camera - After using the camera, your application must properly release it for use by other applications.'

I remember the same problem in a Nexus 4. And Google said they couldn't fix it because it was a bug in a Qualcomm driver and they had no access to the source code.

I think the redesign fixed that because Snapchat no longer takes pictures with the camera. Instead, they take screenshots of the camera preview.

Is that true across the board or just on Android?

If such a problem arose on iOS, Apple would patch it. Android manufacturers don't usually have that option, as they sometimes don't even have the code to the drivers.