It’s literally never happened. There’s never been a miracle that couldn’t be debunked. That’s the problem.
That’s quite the sweeping claim. Prior to a declaration of sainthood, a future declared saint has to have demonstrably interceded on behalf of a believer, or in other words, needs to intercede with God so that a miracle occurs.
In general, before a saint is declared a saint, he or she needs to intercede so that miracles happen at least twice (it used to be 3 times). This must happen after the saint has died. Miracles done in life don’t really count.
The miracle needs to be sudden and impossible by known natural means. If it is medical in nature it goes to a board of Italian doctors.
It also needs be have been done after prayer for the intercession of said saint was done.
This would be hundreds upon hundreds of miracles. Is it possible some may have slipped through that were not miraculous? Sure, but I highly doubt you’ve personally investigated hundreds of rather unknown miracles from just these groups.
This leads me to think that you are, rather, rejecting the plausibility of miracles out of hand. Your name and profile pic make this all the more likely.
But these don’t even include the big, eye-catching stuff like various apparitions and Eucharistic miracles (which we can and do test for human blood and flesh due to modern science!), like
(Wikipedia because it has a list of sources to further expand studies on).
Obviously not all claimed miracles are supported by equal evidence, but a big list of various purported miracles can be found here:
http://miraclehunter.com
We have a skeptical openness to miracles, that they can happen but we should try to eliminate natural causes first. Some people (not saying you) seem to rather use any absurd explanation, even if it is very highly unlikely and nearly calumnious, over accepting the possibility of miraculous intervention.