Not much will break me out of my summer absence. But this is one.
The sad fact of having a decade long experience of dealing with EFB means I can assure you that not all cases are so obvious as showing the contorted larvae etc, especially of they are really good cleaners. Sometimes the larva only dies post capping.
There are other possibilities such as sacbrood..although no 'chinese slippers' visible, or inbreeding, or very severe PMS ....but if we see this we would be looking 50% chance of EFB or 40% of very severe chalk susceptibility combined with being good at removing the early infected examples of both conditions.
No doubt in my mind is that the correct course of action is to call in the bee inspector (urgently!) and get a test done. Irrespective of the outcome I would cull anyway.....this is a defective situation that is not going to go away without a genetic refresh