Hi,
I assume you're referring to the VPN credentials email. If it's something else, specific to that lab, please open a Sandbox Ticket by clicking on the green 'Report a Sandbox Issue' button here --> https://community.cisco.com/t5/devnet-sandbox/bd-p/4426j-disc-dev-devnet-sandbox
If it's blank, that's weird and I've never seen that, and I've seen many of these emails.
If you're not getting the email at all, please check your spam / junk mail folder to make sure the email isn’t there. Did you receive the 1st email only or no emails at all? If your registered sandbox email has recently changed, please let us know.
You can also get the VPN credentials from the 'Output' tab inside the sandbox environment.
