That doesn’t seem right. For something so critical to many of their corporate mega-customers, there shouldn’t be any “third-party managed” infrastructure at all.
You can buy connectivity from 5 diverse providers per data center, but if one of them continues to advertise your routes while not being able to actually pass traffic to your destination, you’re “down” to some people through no fault of your own.
I’ve had this happen with AT&T, XO/Verizon, and Cogent in recent years. It’s not uncommon. In all cases it was mis-configured ISP routers. Usually a support engineer admits a QoS or DDoS-protection configuration went wrong.