several players have mention neither on chat or though messages that they lost Items when they went to evolved their pokemon:

SpectreTrainer said on chat that They lost 5 exp locks, when they evolved their pokemon:

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AnTiN asked me though message, why his Reaper cloth disappear, when he attached is to his Duskull, and evolved it into Dusclops, the item was gone, so he couldn't evolved it into Dusknoir since he didn't have a reaper cloth anymore (but I gave him one of mine so he could).

so I tested out with one of my pokemon, I attached a Sun Stone to my ShinyNumel (who need to be at least at level 33 and doesn't need any specific item to evolved) and evolved it into ShinyCamerupt, and the Sun Stone was gone.

Screenshot:
[you must login to view links] -Before I evolved it, the sunstone was there
[you must login to view links] -After I evolved it, The Sun Stone was gone.

not entirely helping but i think you met either not neither and he/she instead of they

(just thought you may wanna know as you did perfect punctuation on the rest)

Thank you, this glitch has been hopefully fixed.