We had a QuadX8 with 13inch RC Timer props - the IMUs went haywire (or crazy if you prefer a more technical term ) and it went into the ground at speed and about 45 degrees lean. Broke a few props, but all at the tips up to mid-length of the blades. None of them broke near the centre nor damaged the motors or mounts in any way.
I was going to say those washers saved the day - but I just went and looked where I’m setting up those motors and props on a new frame BUT they all just have the allen headed bolts holding the props right to the motors.
So I guess the old Turnigy Multistar 390kv motor are a bit tougher than yours - or I wonder if 16inch is too big for those motors.
You can see a spare set here for ESC testing
Actually the thing to do is sort out the crashing issues before attempting more flights. Those props wont break by themselves
Do you want to open a new discussion with a description of all components and a .bin log file, let’s see what went wrong and step through the fixes.