I noticed the same thing with my two strongest, most productive hives last year, early May.  We have a short dearth around that time, just before the Thyme bloom (in Greece).  I treated with Bayvarol the prior September.  I'm on an island, so no heavy Ag here, thus the wildflowers always outnumber all Agricultural plantings.

I was just looking at the photos I took last year.  A mass of dead drones, various stages in front of the hives.  Live drones being evicted as well.  I picked a few up and put them on the hive cover to inspect and photograph.  All the mature drones had the endophallic symptom you described.

But when I look at the photos of the drone piles, I don't see it. Maybe the rotting drones were easily squished when I picked them up with my heavy beekeeping gloves and that action popped their innards out?  The drone larva/pupa I picked up didn't have that symptom. This is my first post...  I guess I can't post photos on here?

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