Okay, I've just tried it again (in version 9.1.24) and I had the same error. Just check in vendor/lib/hw, when you replace the file "camerasdm660.so", that the permissions of the replaced file are the same of the other files in the folder. (I think r-r-r).I did exactly as you said but it doesn't work. Camera just stops working after these steps, i cant even use stock camera.
The last time I used Solid Explorer and I didnt have the problem. Now I've used Root Browser and the permissions of the file changed when replacing it with the new one. (To change permissions with Root Browser, long click to the file - propierties - permissions)
I hope that can help!