SQL Server connection problem via using sequalize with encryptset to true - node.js

Question

I have been working on a NodeJS project locally on my (Windows) machine which connects to a SQL server database using Sequelize. It works fine on my local machine but when I upload it to an Azure Web App I get the following error on each request..
Failed to connect to x.x.x.x:1433 - socket hang up (IP address replaced with X's by me)
The code is identical and I have checked there are no IP restrictions on the database, it's totally open. I have also checked that the environment variables (username/password etc.) are identical and being loaded correctly in production. In fact, my logging shows that the connection attempt is identical.
The only thing that makes it work is removing the Sequelize/tedious option {encrypt:true}.
So, just to be clear, encrypted connections work from localhost but not from an azure web app.
I have literally no idea why this could be so any suggestions would be helpful, even if they just point me in the right direction.
Here is my sequelize setup. Obviously I've redacted the host IP address and login details but they are the same from dev and production at the moment.
{
'production': {
'username': xxx,
'password': xxx,
'database': xxx,
'host': xxx,
'dialect': 'mssql',
'dialectOptions': {
'options': {
'encrypt': true,
'multipleStatements': true,
'validateBulkLoadParameters': false
}
},
'omitNull': true,
'pool': {
'max': 100,
'min': 0,
'acquire': 30000,
'idle': 10000
},
'logging': false
},
'development': {
'username': xxx,
'password': xxx,
'database': xxx,
'host': xxx,
'dialect': 'mssql',
'dialectOptions': {
'options': {
'encrypt': true,
'multipleStatements': true,
'validateBulkLoadParameters': false,
'debug': {
'packet': true,
'data': true,
'payload': true,
'token': true
}
}
},
'omitNull': true,
'pool': {
'max': 100,
'min': 0,
'acquire': 30000,
'idle': 10000
},
'logging': false
}
}