I can second that, I’m seeing the same behaviour with all my iCal feeds since some time last week.
Sometimes on an refresh all events are imported, but more often than not only a subset of the events in the ICS files appear to have been parsed and therefore, a lot of the events are randomly missing in the calendar display.
As a temporary workaround I have enable the setting to keep events on refresh even if they are missing in the feed. But this cannot be a permanent solution – one the one hand, with the current behaviour, I cannot be sure when an event that I have updated will be updated on the website, on the other hand I want to be able to delete an event and have it disappear from the website as well.