I believe there are significant issues with Battlefield 1 and crossfield. This list Crossfire Game Compatibility List | AMD Crossfire Wikia | Fandom powered by Wikia mentioned it is unsupported in DX12 and has poor performance in DX11. I don't know if that is up to date, and there is a rather large thread on the BF1 forums - I would suggest starting there. SLI/Crossfire issues (Thread for discussion of sli/crossfire issues only) — Battlefield Forums
Crossfire issues are most commonly implementation issues, so its best to start with the authors of the software you are looking to run.
You need to disable Crossfire for this game in Radeon settings>Gaming>BF1 game profile. Otherwise you will suffer from negative scaling effect(you already have it)