Soft Eggs

I know that this has probably been covered loads on the forum, but i thought i would bring it up again.  My two regular layers gave me an egg each yesterday, lucky me!!  I'm sure one off my rhode island red x light sussex is about to start laying.  When i went up this morning i found two separate soft eggs in the bottom off the coop.  Could these be from her?  Her practice eggs.  I get the occastional softie from the other two, but most of the time they are fine.  Last week i had two soft eggs joined together? Is it a case of her not waiting long enough before laying?  I feed them all the same, mush, grit and treats (greens, meal worms sometimes some apple, strawberries etc).  I have some poultery spice, should i treat them all to some?