Hello @louisbohn,
Choosing the “Microsoft CHAP Version 2 (MS-CHAP v2)” appears to have resolved the issue for us
It looks like a windows update at some point had turned that setting off on all of our customers (and our) systems
So now they are showing this
The requirement for this is clearly visible in the guide at Setting up L2TP With IPsec
Thank you for sharing your knowledge and experience. We will keep an eye on it going forward.
Happy to Help,
Marcus 
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