Below is my translation of the ad:
Important announcement for all Daf Yomi learners
With the starting of tractate Moed Katan, R' Chaim Kanievsky said that it is known in the name of the Chasam Sofer that there is a concern in learning Moed Katan because of the fact they you are learning the halachos of mourning. Therefore the Chasam Sofer said that a person should give charity before learning this tractate.
R' Kanievsky added that certainly someone who gives charity to "Kupat Hair" will be saved from any pain and anguish and has nothing to worry about.
As always, the names of all donors will be passed on to R' Kanievsky for a blessing
The mesora that I got from my Rabbeim (RMW, RHS, from RYBS) was diametrically opposed to this approach. They said as follows. Moed Katan and Hilchos Aveilus are just as much Torah as Bava Kama, Zevachim, etc. You are מקיים the same mitzva of talmud torah. There is a chiyuv to know all of Torah and Moed Katan and Hilchos Aveilus are part of that. Therefore, it is inconceivable that a person would come to harm by learning Moed Katan and Hilchos Aveilus when by doing so he is fulfilling his chiyuv to learn Torah.
I remember that in the Morasha Kollel one summer R' Willig learned Moed Katan , half the summer learning Hilchos Chol Hamoed and half the summer learning Hilchos Aveilus with us when we were all between the ages of 18-25. He was not all concerned with this based on what I wrote above.
Here is what the Chafetz Chaim had to say about not learning Moed Katan.
Reb Moshe Bik used to say over the following incident: It once happened in Radin that there were several men that passed away one after the other in a very short span of time. They called a gathering to contemplate as to what was the message that Hashem was sending them.
The Chafetz Chaim arose and proclaimed that the Mesechta Moed Katan is complaining to the Ribino shel Olam that it is a Mesechta that the Yeshivos do not learn. Only mourners learn this Mesechta and that is why many people were passing away.
(Sefer Meir Einei Yisroel 2: P. 239)
Exactly the opposite of the Chasam Sofer, Sefer Chasidim etc.