The UMP wasp probe needed to be restarted following which the umiapi does not respond most of the time.
The wasp.log at level 5 was showing the UMP wasp regularly getting to within 0.5GB of the maximum memory for the wasp probe e.g.
Jul 01 10:30:32:299 DEBUG [ContainerBackgroundProcessor[StandardEngine[wasp-engine]], com.nimsoft.nimbus.probe.service.wasp.WaspLifecycleListener] Memory Status: Max Limit: 4049MB, Allocated: 4049MB, Free: 405MB, Used: 3644MB
Using Raw Configure... (SHIFT+Right Click while selecting the UMP wasp probe)
In the startup -> opt section
Increase the java_mem_max by 2GB to 4GB
Note: Ensure that the UMP server has enough spare capacity after the above allocation in order to continue to operate normally.