Function Execution Time variation.

Performance of functions is erratic e.g.
- Min - 25ms (faster than necessary)
- 50th @ 260ms (slow but acceptable)
- 95th @ 5.4 sec (useless)

The work performed in each execution is identical
1. Accept incoming message from Service Bus Trigger
1. Convert to Hub request
1. Relay message to 6 NotificationHubs in parallel async requests via NotificationHubClient.

The two upstream function also have the same unpredictable behaviour.

This function is part of a chain that needs to be timely (not fast) and it is therefore materially affecting the user experience.

#### Investigative information

- Timestamp: 09/01/2019, 11:57:05
- Function App version (1.0 or 2.0): 2.0 - F# pre-compiled (run from package)
- Function App name:
- Function name(s) (as appropriate):
- Invocation ID: jEGcMsArsWI= cf85ff6a-efab-40e4-bc8c-fad7bb98d47e
- Region: UK South

#### Repro steps

The issue is not reproducible - but is frequent (50% of executions are slow to staggering).

#### Expected behavior

Consistent execution time with smaller variability.

#### Actual behavior

As described.

#### Known workarounds

NONE - We are considering reverting to or V1 code as it had more reliable performance.

Start with the reported Function App version, UK South region, invocation ID, and the Service Bus Trigger to NotificationHubClient execution chain. Compare the stated minimum, median, and 95th-percentile timings for the upstream functions and downstream notification requests. Done means identifying the cause of the frequent latency spikes and establishing consistently lower execution-time variability.

Written by the indexing model from the issue text.