So this has probably been talked about a few times (I've only seen 4 posts probably under a different name) but I have one feild guide page missing its in the great hall. I've been through that place literally fine tooth combing it, I even took to watch YouTube videos and did a full follow through of every spot. Still I got nothing I've heard about the bug but I've only seen the green house and the bell tower. I can't find the bug for thag either which is weird.
#field guide pages
rose sleet
acoustic sigil
SAME! I'm playing right now, and I opened discord to ask for some help. Seems that we have the same problem. I went through the playthroughs twice already and it's still missing one page! I'm playing on the PS4 though
shrewd island
honestly i tried to look up for the solution to this but on pc and its either a hit or a miss otherwise go through some complicated way to somehow make it work. Im not sure what the case is for you both but if the field page does not fall under the collection tab you should at least be able to get the achiev. since the one i couldnt get was a moth page and i still managed to 100%