Nuclear warnings have been overused a little by some actors in the past, such that there's a credible risk of someone calling the bluff and continuing research in secrecy, knowing that they will certainly get another warning first, and not immediately a nuclear response.

If you have intelligence that indicates secret ASI research but the other party denies, at which point do you fire the nukes?
I expect they would be fired too late, with many months of final warnings before.