Different smartthings accounts are on different “shards.” ( you can think of those as database servers.)
The “graph.” Shard Was the original. Then when they added UK accounts, there was a UK Shard. Towards the end of 2015, the original North American shard became overcrowded, and they added a second North American shard, NA02. There was also a beta Asian shard at one point. So different customers are on different shards.
When they first introduced the UK hub in the fall of 2015, it didn’t work with IFTTT because the connection URL was incorrect. But they eventually fixed that, and, as mentioned, added an additional North American shard, and all three worked fine with IFTTT throughout 2016.
The current problem that people are seeing is something new. But it sounds like it isn’t affecting everyone, which is why engineering would like anyone who does have the problem to report it to support so they can see if they can isolate the issue.