Pure speculation but a mundane explanation for so many drones, rockets and missiles getting past Iron Dome could be simple mechanical wear and tear on the launchers, radars etc. It has been operating pretty much non-stop for a year, that's going to cause some degradation.

also it's really only designed for the sort of janky homemade shit hamas have been able to muster. was never designed to keep out the sort of thing they're facing now afaik