Just as an FYI for you since you tried to help (and others if they have this issue) and if you have other users asking about it. I fixed the Google Camera modded apks crashing.
As mentioned in this thread (https://www.google.com/amp/s/xdaforums.com/mi-5/themes/app-collection-camera-modded-t3591177/amp/) there are 2 files that have to be deleted after flashing certain gapps.
/System/framework/com.google.android.camera.experimental2016.jar
and
/System/etc/permissions/com.google.android.camera.experimental2016.xml
Ohh... Reminds me though, I had those files installed while trying to get my own GCam installation to work, and yes I also met FCs. Didn't know some GAPPS would bring this with them too. Thanks for letting us know.
Sent from Xiaomi Mi Mix 2 @ LineageOS 14.1