>So Meraki support bumped the key exchange up to DH14 and it worked.
Just to play devils advocate, one end (the MX in this case) offers the encryption settings it is prepared to accept. The client chooses and then says "I would like to use this" and they continue on.
Lets say DH2 and DH14 were offered but your client only supported DH2 - it will connect using DH2. Just because you have something strong enabled does not imply it is being used.
I don't know how to verify it - but if it is important you should find a way to verify the settings that Windows 10 has actually negotiated. Alternatively, you may need to find a way to configure the client to only use a specific set of crypto settings.
Otherwise it may not choose something just because you want it to. 🙂