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Thank you for your reply!

Yes, temperature during a critical period of development could be the key factor.

BTW some Antiphrisson shown on Flickr under the name A. adpressus are indistinguishable of these "thalhammeri" of mine, so their identity is also questionable:

https://www.flickr.com/photos/superegnum/51453752028/in/photostream/

https://www.flickr.com/photos/superegnum/51468673209/in/photostream/

Interestingly, those photos were also taken in autumn (middle of September).