Do you mean the transiting ascendant is sextile your natal vertex? That happens every day. Twice, in fact. The ascendant makes a complete cycle of the zodiac in slightly over 24 hours. That means it will sextile every point in your natal chart twice in each 24 hour period. And trine every point twice, square every point twice, oppose every point once, and conjunct every point once.
In and of itself, that's not a meaningful transit. When it might be meaningful is if you're looking at an event chart for the moment when a particular event happened to you (you unexpectedly ran into an old friend, you got into an accident, you got a phone call saying you'd won an award, something like that), or if you're casting an electional chart for a planned future event. Even then, though, an ascendant/vertex sextile is just a minor note. What's going on with the planets would be more pertinent.
Anything else you might mean would be impossible. The vertex doesn't really transit, although some programs show one in a transit chart, because they're calculating every possible point at every given moment. And the vertex is, by definition, always somewhere between the fourth house and the tenth. It cannot sextile the ascendant. Now, if you overlay the transits of the moment on your natal chart, the vertex of the moment could be sextile your natal ascendant, but that can only happen when the transiting ascendant is on the other side of the zodiac from your natal one.