Matt - as a newer user, welcome to CityStrides.
I am by no means an authority, just an enthusiast like you, but as I understand it there are a few things at play.
You are part of a MONSTROUS wave of new sign-ups starting last month. Most of those sign-ups use Strava as their activity source.
Strava severely limits how many times CityStrides can access information per day (API Calls). Currently, the
number of new activities per day combined with the activities part of historic account syncs far exceeds number of times CS can access it each day when you factor in new activities and synchronizing full histories for the new waves of members. See the Status Page, with more information about that page in the Wiki
Supporting members are valuable as they help support the development required to resolve the issues, and they also receive prioritization in activity retrieval (among other perks).
Solutions are being sought, hopefully it can all be remedied by a combination of help from Strava and expansion of what services users have the data come from. See @JamesChevalier efforts here.
I know it isn’t a great answer, but it is the current situation.