This has been happening on and off for years. gCal stops updating subscriptions.  You add a new URL and it will pull all of the events but after that new events will not appear in gCal.  Then one day... it starts working.  Maybe for months, then.... it breaks again.

It's hard to recall accurately but I'm pretty sure I've seen this happen at least three times in the last 5-6 years.  The question is... how long will it last this time?