Hello, playing with installation FP2 on machine with CU4 end with :)


and based on info found https://blogs.msdn.microsoft.com/biztalk_server_team_blog/2017/11/21/microsoft-biztalk-server-2016-feature-pack-2/
You can install Feature Pack 2 on BizTalk Server 2016 Enterprise and Developer Edition (retail, CU1, CU2, CU3, FP1)
I recommend to uninstall CU4 in case you not facing any issue described in that CU and install FP2 with CU3 or maybe wait when FP2 will be with CU4.