Well, indeed you are not the first user “stepping back” to Marshmallow.
Too sad, but despite of Fairphone’s efforts at last it’s not all their fault, but rather unforeseen massive troubles that came up due to the missing “support” of Google & Qualcomm which in former Android Version delivered proprietary device drivers which Fairphone now have to “replace” (re-program) all by their self. Unfortunately this task is bound to any “individual” platform and code cannot simply be copied from another phone out there. 
Many functions therefore are (still/again) missing or unwanted behaviour often is interpreted as fault.
FP is putting a lot of energy into getting Android 7 running as satisfactory as possible, but time does not stand still and many users are complainting about their disappointment with the Android 7 update.
Well, if being used to having a flawless operating phone not wanting to test out if the individual (software) setup will work reliable, I think Marshmallow is still the best alternative to chose. Maybe even LineageOS may meanwhile do a good job which btw. is based on Android 9.