SSL warning message from a specific VLANs?

Hello guys, i need your help please! My clients are getting SSL warning message on thier website from specific SSIDs in the network! But as soon as thry enter the site and switch to other SSID and refresh the page, the warning message disappears! This is actually occurs when accessing the website from specific SSIDs and when connected to network with Ethernet cable. When accessing the website from outside the network its fine and you won't get the certificate warning. I reached out to the host providers support and they confirmed that its not from thier side. *They are using Cisco Meraki appliances. I appreciate your help! Thanks