There's a couple of things we can try, but can you first please run the VIRL Server Salt Connectivity Validation script and reply back with the results. This will give us a better idea of your current configuration.
Then, please review and apply the appropriate Salt Masters listed on the following post: ATTENTION: Salt Masters Update (Licensing)
If that doesn't work, let's try changing the MTU size. Please refer to the following thread and solution: Failure to activate new instance of VIRL
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