I have not been sure if these issues are due to delays in the system, so if it seems patience will solve this, that is fine. Partly this is complicated by recent changes with Fitbit, Runkeeper or both.
Briefly, I started letting activities sync from Fitbit to Runkeeper since I got a GPS Fitbit. Sometimes I open the activity in Runkeeper to add a description. Resaving within RK causes the GPS points to smooth a bit, and the distance changes. Perhaps related to that, the activity will resync from Fitbit and cause a duplicate. I have not fully investigated that yet, but for now have been deleting the duplicates in Runkeeper.
That has resulted in my needing to also delete activities in CityStrides. My assumption would be resyncing CityStrides would cause anything in my RK to end up back on CS even if I deleted it previously.
Currently I am missing the last bunch of days of runs on CS, and one of them that is there is showing 5 times, at https://citystrides.com/users/2455. I am fine with clearing the last month out and resyncing with Runkeeper, which is my source of truth currently.