I've used Zuora for about 10 years now - spoke for them at their Subscribed events, Dreamforce, etc. The top 3 issues that continue to recur:
1. Under pressure to deliver wall street results, they pass that along to their customers upon renewal. It's never about how can we make sure you're happy and we're charging you based on the value received, but it's about retaining ACV and trying to grow ACV from each customer every single year. And their tactics are dirty ones that I've never experience from any other vendor.
2. I've had multiple challenges with their professional services in the past (granted, the last engagement was about 4-5 years ago now).
3. Their platform data model is complicated, so it can be difficult to figure out how to pull billing metrics from it. Review collected by and hosted on G2.com.