HttpTrigger Function response unexpectedly slow

HttpTrigger function that normally returns sub second, either hangs or takes minutes to respond.

#### Investigative information

Please provide the following:

- Timestamp: 2018-01-17T22:14:38.927Z
- Function App version (1.0 or 2.0-beta):
- Function App name:
- Function name(s) (as appropriate):
- Invocation ID: 1aa45b13-e2b4-48bb-a063-ddd54c516000
- Region: EUW

#### Repro steps

behaviour was random and occurring regularly on 2018-01-18 from 20:00

#### Expected behavior

Sub second response

Start with the reported timestamp, invocation ID, EUW region, and the HttpTrigger behavior described in the issue. Review the missing Function App version, app name, and function name details before investigating the random delays. Done means the cause of the multi-minute response is identified with a reproducible set of conditions.

Written by the indexing model from the issue text.