I have a COM domain with several subdomains. These subdomains have CNAME records pointing to
ghs.google.com (they point to different Google App Engine apps). These have been in use with no problem for a few months.
Recently, however, I've started receiving reports from some users that they are no longer able to connect to my apps. I've discovered that
nslookup subdomain.domain.com is failing for these users (for all of my subdomains). Many of these users are from a Singapore-based ISP called StarHub, though others are scattered across other ISPs in places as diverse as Argentina, India, and New Zealand. I haven't received any complaints from US-based users (the biggest segment of the user base). Most users seem unaffected by the problem (based on traffic levels).
Any ideas of what the problem is, or how I can fix it? I've tried contacting some of the ISPs but they've all been a bit unhelpful (insisting that the problem is on my end).
It is worth noting that the users experiencing problems are still able to connect directly via an IP address, or via the appname.appspot.com subdomain (provided by Google App Engine) - just not my subdomains anymore.