Here are some general things to check:
LINQPad activations on virtual machines are tied both to the machine and the underlying hardware, so if the latter changes, the activation may become invalid.
When activating, choose the option to activate all users (rather than the current user) unless you plan to always use the same login.
Activations on Azure VMs are not fully supported on versions prior to v4.47.05, which is still in beta at time of writing.