Does the resource usage of a hypervisor host affect a guest server?

Question

Answer

Yes, if the hypervisor has run out of resources such as disk space, memory, or CPU time, the guest machine's performance will suffer, or the guest machine may even crash in some cases.

The %steal metric on a guest machine can sometimes provide clues when the hypervisor is low on CPU resources. You can read more about this here:

What is CPU steal and when should I be concerned about it?

The following guide also has valuable information about diagnosing high load:

How to diagnose high server load