ESXi 6.0 Express Patch 6 (build 3825889) released to fix the Purple Screen of Death (PSOD) with VMXNET3 vNICs breaks also CBT in some scenarios.
Same patch broke Veeam Instant VM Recovery and Veeam was quick enough to release a hotfix.
This CBT issue is affecting users not using Veeam's application-aware processing (VSS) and with VMware Tools quiescence enabled in the advanced job settings.
The Enable VMware Tools quiescence option in the advanced job settings.
Unfortunately vSphere 6.0 is not stable enough and this recurring CBT issues are causing lot of problems to the users. This is one of the reasons why some administrators didn't migrated their environments to vSphere 6.0 yet.
Hopefully the upcoming new vSphere release will bring a better situation.
Update 27/06/2016
VMware published the KB article about the latest CBT issue KB2145895.
