If you happen to stuck with any issue with the Dual-write implementation from on how and where to start with dual-write - The source of truth is a yammer group https://www.yammer.com/dynamicsaxfeedbackprograms/#/threads/inGroup?type=in_group&feedId=16038053 runs by Microsoft Dual-write product team.
FILES tab in the group contains all A-Z documentation.
Get your questions answered today by various experts including MS dual-write product team.
You can even raise your live issue with them in the yammer group and they connect with you in no time - very much useful!!