Are they all the same variety, Coachman?

yes i assume so as i grew them from seed all from same packet & a reputable supplier

Well, unless there was a mistake at the packager's, then the two different ones probably have some difference in culture:

Are the pots the same size as the others? Are the pots made of the same material as the others?
Is the soil from the same batch as the others?
Are they in a position where they may be forgotten as to feeding or watering? If you are spraying the food on, are they at the end of the line so they may be getting the dregs of the food?
Are they getting the same sun exposure as the others?

There may be other differences, and sometimes even the smallest divergence could be critical.

Another possibility. Did the seeds come out of the packet in different colors? Some of the older burpless greenhouse cucumbers have two varieties in the packet: the variety that you harvest, which you remove all the male flowers from; and the pollinating variety, which is used to stimulate the female variety to produce seedless fruit, and produces low quality fruit itself. The different seeds are marked with colored dyes, but the procedure isn't always laid out well on the packet.