I tried searching the forum for this and haven’t seen something like this posted yet, so please forgive if this is a known bug.
I had Panharmonicon on the board, then cast Thunderherd Migration. Instead of fetching my next copy of Thunderherd, it instead fetched a copy of the first card in my hand, Hazoret’s Undying Fury. I think it’s happened to me other times, this was just the first time I’ve been able to definitively identify it and get a screenshot to prove it. (Unfortunately the battle log only says that “Panharmonicon was triggered”, it doesn’t say what it fetched.)
I’ve submitted a ticket with screenshots so the team was aware, just wasn’t sure if this was a known issue or if anyone else has run into it.