If you are using a google calendar ics file as event input you should be aware of the following:

• the ics file may get rather large over time.  At time of writing there is no way to get the feed to only show future events, so it will have ALL your old data.  This all has ti be parsed, turned into event data and held in memeory to see if there any any modifications, or exclusions.    If you don’t need the old events, try deleting them.  You may need a bulk delete tool.  I have used this GcalToolkit, not ideal but it does work.
• At times the ics feed used to be slow to update – check what the actual feed contains if you think events are missing .  Open the ics file in notepad, and check if your events or your changes are there.  Note that an instance may have multiple VEVENTS with incremental SEQUENCE numbers later in the file.

On the other hand, when using an amr-events feed in a google calendar,  google can be slow to refresh reading the feed, sometimes it will do the first one fine, then you make a change and expect google to show in instantly.  It will not.  Not much we can do about that.