Hi @Tudor_Butiulca, So, the Meraki APs will only push the splash page to the client when they see HTTP traffic coming from the client device. It is possible that on windows 8.1 and windows 10, Microsoft has introduced a to send HTTP traffic by default to trigger the splash page which might be missing in Windows 7. A packet capture will confirm this behavior.
I did a bit more research and it seems like Windows does indeed check a Microsoft site for connectivity, using the Network Connectivity Status Indicator site (NCSI). There are a few variations of the connection checking process:
NCSI performs a DNS lookup on www.msftncsi.com, then requests http://www.msftncsi.com/ncsi.txt (HTTP file). This file is a plain-text file and contains only the text Microsoft NCSI.
I would recommend to take a packet capture and see if the NCSI packets are being sent by the windows 7 device and if so, we need to further investigate on the Meraki side. If the windows device is not sending those packets, we might want to check what service pack is being used and make sure it is up to date and check what is breaking it.
Cheers!
Raj
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