I’ve been having this issue trying to delete some runs from Dec. 22 (5 days ago).
I wasn’t sure if I caused the problem for myself because I was fighting some automation syncing a run from my Fitbit account to Runkeeper to Citystrides. I had to delete the run from Runkeeper twice before then trying to delete from Citystrides. One finally disappeared after 2 days but the other is still there on CityStrides at Charlie Gorichanaz's activity on December 22, 2022 - CityStrides, and it’s been gone from my Runkeeper for 4 days. I triggered a new deletion on CityStrides about once a day just in case the queue got dropped.
I see on https://citystrides.com/status the “Slow Jobs Delay” is multiple days. Something must have broke, but I figured it wasn’t worth disturbing anyone’s holiday break over. 
I did see a recent post by @nurseangel72 on Deleting Activities - #26 by 8f7162110d9eeaf907ab , so it may be a recurring issue recently.