Appears Black and White squares errors when Bake lightmap

I have the same problem but it's just white squares, and those white squares produce tons of light onto the scene like they are atomic explosions. I'm not usually baffled by lighting issues these days but randomly occurring (from bake to bake) self illuminating squares (when there's nothing in the scene that would cause such a phenomenon) is just as likely to get solved as your question. See the problem with Unity's community is that ALL graphical phenomenon issues are inherently difficult for users to articulate questions about and for members to search for answers to. Things that are VISUAL can be named or labeled in infinite ways and these forums are stupid when it comes to helping people solve visual problems. Don't expect a solution either because almost all visual problems are so repetitively asked that members feel like you should have just found the already-answered version of your question or perhaps that members won't ever find your question because there's a continually growing glut of unanswered questions a mile long and yours is nothing easy or too special to not answer. Good Luck...meanwhile I hope some brilliant human at Unity is taking note of the problem with trying to search for answers to visual phenomenon in these forums. My suggestion to them has always been to create a visually laid out interface where few words are used and instead visual representations of what you might be experiencing is shown (think google image search results) in a large grid of many many images that show off (and highlight) the section of the image that is discussed within the picture if you were to click on the picture. Once the link is clicked there may be subcategories of nuanced issues relating to it. This way similar questions or exact same questions can be resolved within one defined area that people can read and get full answers to. But I've explained all this 2 years ago and Unity obviously has done nothing to revolutionize one of the most common problems with asking questions - knowing how to ask the question with the right combination of words, otherwise you don't find the solution to your problem and worst of all - you don't know if you're the first person to ask the question or if you simply aren't asking it the right way in order to find dozens of already-answered threads - and it's the "not knowing which of those options is the case" that is causing an inflation of this gigantic collection of threads and growing number of unanswered questions. Do your job Unity!

Did you ever find a solution to this? I only get it with the progressive lightmapper

It also happened to me, I tried to place the rectangle of the area light that does not protrude outside the object to be illuminated, the square of the area of light must be equal to or somewhat smaller than the object itself.