Saving UCS on VCMP guest hangs up

11.6.0 has a detailed statistics reporting engine for troubleshooting guest details. Maybe this will help?

"Description

As of BIG-IP 11.6.0, the vCMP hypervisor can view detailed guest performance statistics such as Disk usage, CPU usage and Network Throughput using Analytics, also called Application Visibility and Reporting (AVR). You can use AVR to view current and trending data regarding vCMP guest resource and network utilization. You can generate PDF reports and either downloaded or email them from the BIG-IP system."

https://support.f5.com/kb/en-us/solutions/public/15000/600/sol15684.html

My two cents: if all four guests are running on the same blade, and the blade has a disk (not SSD), you might have better results by running a staggered ucs save. That is, do guest 1 and only once complete beging the ucs save on guest 2. This would avoid what appears to be a problem with initiating a save on guest 1 and 2 at the same time. (probably not what you want to hear, but this should be functional until the concurrent save issue is sorted out.)