Notice that this has literally led to the expulsion of diplomats, or, I suppose, spies sent out under diplomatic cover.
That's extremely unusual between allies. Spying on allies, trying to bribe or blackmail their personnel etc., is not normal. It makes you a security threat, and making oneself a security threat isn't really compatible with being allies.
Presumably this is why there is now this very public declaring of diplomats persona non grata-- both to remove the people in question and to signal that what has been done isn't okay. Seen another way-- normally, the person who becomes persona non grata is a Russian.