I think the problem that some people are facing after flashing the zip, is recovery - specific or recovery related.
Actually I never had to perform a clean flash of my ROM.
So try the following:
1) Flash the camera zip only after flashing ROM and gapps (whether clean flash or dirty flash does not matter).
2) Flash camera zip twice, clean dalvik + cache, and reboot. Still same problem then, reboot to recovery and try same thing again.
4) If you are using TWRP, then you need to mount the system manually before flashing the zip.
5) Switch recovery to some other. If using PBRP, update to the latest version. Or otherwise use OFRP. Its what I use.
6) Don't use stock gapps after flashing ROM. Use other gapps. You can use micro gapps. Its what i use. Stock Gapps is known to replace camera apps.
Also, flashing gapps is required only if you are doing a clean flash. During a dirty flash, flashing gapps is not required at all.
7) If still none of the above work for you, then the last resort is a clean flash.