Q. I was at a synagogue near home, and the Rabbi said a tissue box there could not be used. Why not?

A. Not being there, I can’t be sure, but it probably was an issue of tearing on Shabbos. If the tissues were connected, there may be an issue of tearing them apart on Shabbos. Some Rabbinic authorities allow tearing tissues/toilet-paper as long as it is not torn on the perforation (since that would be tearing in a measured and exact way), but others do not allow any tearing of tissue or paper, even not on the perforation. The tissues in the box must have been stuck together.