C# Functions Not working after upload to Slot.

Steps:
Create deployment slot from Powershell (or maybe other way too did not check yet).
Deploy Working .Zip package through Powershell:
```
$apiUrl="https://$functionAppName-$functionDeploySlotName.scm.azurewebsites.net/api/zip/site/wwwroot"
Invoke-RestMethod -Uri $apiUrl -Headers @{Authorization=("Basic {0}" -f $base64AuthInfo)} -Method PUT -InFile $zipFilePath -ContentType "multipart/form-data"
```
Checked on Kudu All files are 100% fine.
Javascript Function is picked up and working OK.
C# is giving 404
**Swap Slots ... deploy->production**
C# and Javascript Working 100% fine on Main (production)
**Swap Slots ... production->deploy**
C# is giving 404

Error popping up (don't know if connected):

> We are not able to get the key swaggerdocumentationkey. Please check the runtime logs for any errors or try again later.
> Session Id: f32a3f07e9874f35967c2361a97f4add

and (which is NOT TRUE host.json is empty!!!):

> Value for id has been explicitly set in host.json, which may cause unexpected behavior when using deployment slots.