UPDATE:
Re my Sierra issue: despite several back-and-forth postings with Sierra support board, they did not help; but later I solved the problem.
For some reason, from one Sierra "disconnect," again about 4:15 pm each afternoon to the next morning, on just 3 - 4 future symbols, there was an option that went to NO, which I always had as YES, related to incorporating data from overnight. Apparently that YES also will backfill from when I start Sierra about 5 am, using data from 6 pm prior night.
Why Sierra support did not query if those options were all set to YES, I can't explain. Still, it may have been a bug in their new program, as I had to download their newest version, in order to adapt to the change in IB exchange ID. (IB changed GLOBEX ID to just CME.)
Mark, re CQG, I used them for several years, & preferred their ladder / BookTrader vs IB, but I always had IB account, order entry, & Sierra charts, also open, as a backup, for the many times I could not place an order via CQG. CQG, whether downtime, change in features, etc, was no more stable than IB. That may have changed over last time I used CQG, about 7 years ago.
Whether IB, CQG, or any of the dozen of other platforms I've used over many years, I never understood why they do not send a text, or e-mail to all users, that they are having problems. There have been times where IB is down, & active discussion on this site about issues, but going to IB "System Status" page has no indication. Just poor customer service /tech support, but seems universal.