DX APM SaaS and On-Prem 21.x
This is an indication of an EM hardware resource issue (CPU)
Next time the issue occurs, monitor in parallel:
1) the raw metric
2) the affected calculator (showing 0 value)
3) below EM/Collector supportability metrics:
"(Virtual)Custom Metric Agent (Virtual)|Enterprise Manager|Internal|Calculator Harvest Time(ms)"
"(Virtual)Custom Metric Agent (Virtual)|Enterprise Manager|Health| Harvest Capacity(%)"
NOTE: to better monitor this unexpected condition, create alerts based on the above 2 metrics, you would need to check their historical data to be able to set the appropriate thresholds values.