Maybe you could ask this in the AMA tomorrow? https://www.reddit.com/r/BuyFromEU/comments/1loy4ql/ama_fairphone_this_thursday/
Also, please consider submitting a support ticket, if you haven’t yet: https://support.fairphone.com/hc/en-us/requests/new
Relevant thread in this forum: FP6 Refresh rate dropping seemingly random