I am sorry I cant get in to specifics. But Routing for GGC is controlled by Google, it is not out of ordinary for your google traffic to not come directly from the GGC node of you ISP. Any internal routing change by your ISP might also cause your Google traffic not coming from your ISP GGC node.
There are too many variables its hard to tell what exactly caused your issues.
But generally speaking GGC nodes are very reliable, their support is responsive and knows what they are doing very well and most importantly it saves us insane amount of money (cause BW is expensive here), and our users are getting better service.
Yes of course, the main traffic is youtube bw, which I think its 95% of the total traffic going through ggc nodes. But the don't have a breakdown of their traffic on GGC dashboard. We know it because we know our traffic before we had GGC and after we had GGC.
There are too many variables its hard to tell what exactly caused your issues.
But generally speaking GGC nodes are very reliable, their support is responsive and knows what they are doing very well and most importantly it saves us insane amount of money (cause BW is expensive here), and our users are getting better service.