Empty triggers sync after 'D:\home\site\wwwroot\host.json' reading error

#### Investigative information

- Timestamp: 2020-09-30 07:51:48.6859060
- Function App version:
- Function App name: [not sharing]
- Function name(s) (as appropriate): [not sharing]
- Invocation ID: N/A
- Region: [not sharing]

The App name etc. can be identified from this query:
```
cluster('wawsweu.kusto.windows.net').database('wawsprod').FunctionsLogs
| where TIMESTAMP > datetime(2020-09-30 07:50) and TIMESTAMP < datetime(2020-09-30 09:05)
| where Summary has '8bd87703-806d-41ea-a471-c9cc6652ad7f'
```

#### Repro steps

The issue is intermittent and rare, no reliable repro steps.

An app using Service Bus trigger worked correctly until a Functions host failed to read host.json (apparently because of transient file system availability issues): `System.IO.IOException : The network path was not found. : 'D:\home\site\wwwroot\host.json'`

The host restarted and retried multiple times. Suddenly, it sent SyncTriggers with an empty lists of triggers and functions:
```
Making SyncTriggers request (RequestId=8bd87703-806d-41ea-a471-c9cc6652ad7f, Uri=https://[removed app name].azurewebsites.net/operations/settriggers, Content={
"triggers": [],
"functions": []
}).
```
This sync requests succeeded, and the app triggers stopped triggering. A few seconds later, the host loaded host.json successfully, but did not send SyncTriggers anymore. Eventually, another Functions host started on a different instance, loaded host.json successfully, and synced triggers properly, so the app self-recovered. However, there was a long period of time (more than 1 hour) when triggers were not triggering.

#### Expected behavior

On 'D:\home\site\wwwroot\host.json' reading error, the host is expected to keep retrying, but not erasing the existing triggers.

#### Actual behavior

The host sent SyncTriggers with an empty lists of triggers and functions.

#### Known workarounds

None

Start by tracing the host.json loading path and the SyncTriggers request to /operations/settriggers. The issue provides no repository source files or reliable reproduction steps; done means a host.json read failure does not send an empty trigger list, while later successful loading still preserves or restores existing triggers.

Written by the indexing model from the issue text.