One issue I have seen in distributed systems is where a library is on another customer/teams hosts and brings them down due to a bug in the library. The other customer/team has no way to fix the bug and is dependent on getting the attention of the company/team who vended the lib in the first place. One I remember is where a library had a bug which created 0 byte files and exhausted the inodes causing an outage.

Cloud systems have become cheap enough and flexible enough that protecting your customers by not putting your bugs on their hosts is not as big as a lift as it used to be when you had buy bare metal servers or explicit VMs.