New sets of young M dwarfs with complex, sharp-peaked, and strictly periodic photometric modulations have recently been discovered with Kepler/K2 and TESS. All of these targets are part of young star-forming associations. Their nature still poses a puzzle, with suggested explanations ranging from (i) co-rotating clouds of material to (ii) stellar spots getting periodically occulted by spin-orbit-misaligned dust disks. Here, I will provide a comprehensive overview of all aspects of these hypotheses, and add new observational constraints to understand these objects with photometry from TESS and the SPECULOOS Southern Observatory (SSO). I will scrutinize the hypotheses from three different angles and discuss: (1) the plausibility of their occurrence rates; (2) the longevity of these features over one year of observations; and (3) the observed color dependency. In this process, I will also revisit the stellar parameters accounting for activity effects and discuss stellar flares as activity indicators over year-long time scales. Adding these and other new pieces to the puzzle will ultimately enable us to unravel the mysterious nature of these young M dwarfs.