I used 5x Max7219 LED matrices for this project. During testing I had issues with LED rows dropping out or LEDs going off and on. It turned out that while daisy-chaining the LED matrices together, power drops after 4 matrices. I solved this by powering the first 3 via the initial cables, then adding a separate power line for the last 2.
...now I know why they are sold in packs of 4.