%RDY below 1 but %CSTP in the hundreds (e.g. 177)

I have read plenty of docs and blogs that explain what %RDY and %CSTP are and indicate that when you see them both high then you are probably CPU over allocated or over committed:

There is also indication that when you see %CSTP high on its own that there may be snapshot consolidation problems.

However I have three 4 cpu 16gb MSSQL VMs with no snapshots. The experience seemingly random periods of poor performance. During this period %RDY is not above 5 but %CSTP is in the hundreds (e.g. 177).

There are no snapshots.

Anyone able to point me in the right direction to help me diagnose this?

Thanks in advance.