The Cambrian Explosion is, of course, the star example:
In 1991, a team of paleontologists concluded that the Cambrian explosion “was even more abrupt and extensive than previously envisioned.”
The abruptness seen in the Cambrian explosion can also be seen on smaller scales throughout the fossil record. Species tend to appear abruptly in the fossil record and then persist unchanged for some period of time (a phenomenon called stasis) before they disappear. In 1972, paleontologists Niles Eldredge and Stephen Jay Gould called this pattern punctuated equilibria. According to Gould, “every paleontologist always knew” that it is the dominant pattern in the fossil record.6 In other words, the “inconceivably great” numbers of transitional links postulated by Darwin are missing not just in the Cambrian explosion, but throughout the fossil record.Jonathan Wells, “Top Scientific Problems with Evolution: Fossils” at Evolution News and Science Today (February 12, 2022)
Where the needed transitional fossils are missing that matters most is researchers’ willingness to be honest about what their absence means.
You may also wish to read: Evolution problems: “Species” is such a mess of a concept And evolutionary biologists keep looking for examples in nature, with meagre results. One way of attempting to demonstrate speciation is to seize on inconsequential genetic changes and inflate their importance.