I am sorry for the bad hatches!Ive been using the same bator for years my eggs are clean when put in I don't get why all of a sudden they won't hatch
The most likely cause is that the incubator has gone out of calibration.
Banty is correct too--Sanitize everything and look into getting a new incubator.
My Brinsea Octagon 40 is supposed to go back to them every two years to be checked over.
Incubators do not last forever.
It does not sound like a flock problem. If you picked up fertile eggs from another source they would likely die like that too