I do have more or less exactly the same issue; tried Camera and OpenCamera and the flash isn’t working either, nor is the torch function.
On a more or less unrelated note, the front camera also does far too dark images with the standard camera app, though OpenCamera does just fine here (so this seems to be a software issue).
I’m still running 17.08.1, does anybody know whether there were improvements in 17.08.1.1 to the camera functionalities (don’t see any mentioned here: https://code.fairphone.com/contentx/2017-08-22_fairphone-open-17.08_release.html).
Edit: Just tried de- and reattaching the camera module, and it didn’t change anything about the flash.
Edit 2: I just updated to 17.08.1.1, and now the flash works fine! Just the front camera still shows a far too dark image in the default Camera app (but works still in OpenCamera, so it’s fine!). Not sure if this is a white balance issue or something else… have to test that in daylight conditions tomorrow…