Might you have possibly cooked the bottom of the jars while sterilizing? I am just now getting back into growing but if I remember correctly I once had the same thing happen and the kind ppl that turned me onto this hobby told be that in their experience that when the bottom of a jar doesnt colonize and you worked clean.... it is due to overheating/cooking the jars in the bottom of the PC/rack did you run low on water in the PC?
mine still turned out fine I just trimmed the bottom off after the rest of the jar fully colonized then put em into the FC
mine still turned out fine I just trimmed the bottom off after the rest of the jar fully colonized then put em into the FC