If these are Dell machines make sure you remove SmartByte.
https://community.meraki.com/t5/Network-Wide/Dell-Laptops-and-VPN-access/m-p/12826#M321
Device is not trying to VPN in from behind the MX?
Windows 10 Pro?
Is Xbox Live Networking Service off?
Also to verify you have encryption set to optional, not required on the adapter properties?
Any other 3rd-Party Software affecting these systems (Endpoint security, AV, etc.)?
Tried limited boot with majority of services/programs disabled?
Uninstalled any existing VPN software?
Checked Windows Reliability Monitor for recent updates/issues/performance?
Tried network reset? (netsh int ip reset)
Have you tried a different device to VPN in with? (using a phone helps to rule that it an MS issue and not Meraki )