Resolution:
The diagnostic messages in the GridServer 5 Manager log memory and thread status of the Manager. For example,

17/07/08 14:25:28.703 INFO: [DiagnosticsPlugin] [M: 479M/583M/1365M] [T:D(19) O(150)] [5.0.0.53]

Interpret this example message as follows:

[M: 479M/583M/1365M] = [Memory: Amount of used memory (totalMemory - freeMemory) / Total amount of allocated heap memory / The maximum amount of memory available for allocation to the heap]

[T:D(19) O(150)] = [Thread: number of active threads/ number of unmonitored active threads]

[5.0.0.53] = [version number of gridserver]]