I've noticed that for my usual API call of https://weather.visualcrossing.com/VisualCrossingWebServices/rest/services/timeline/Ottawa,CA?unitGroup=metric&key=<KEY>&options=nonulls&include=fcst%2Ccurrent,obs that most of the nearby airports have disappeared and I'm left with these two stations:
EW3670 Ottawa CA : "distance": 1926
KMSS : "distance": 86364
This means that the only source of cloud cover data is coming from a station ~86km away from me which is not the most accurate for my location. I checked a few other locations in Canada and around the world and it seems to be an issue outside the US though I can't say for 100% certainty that this is correct.
Some locations if there is no station reporting cloud cover data it comes from somewhere else since they are too far away to find a station with this data. I did find that the conditions seem to not match using this other data.
This started a few days ago and I haven't seen anyone else post about it so it must not be a known issue.