Suggestion: Liber de Monstrorvm
I don't know if this is the right place to post this as the Feedback tab on the official website has been turned into the community Discord link.
But overall my problem with the Liber de Monstrorvm is that it is woefully annoying. As it is right now, when you are supposed to kill lets say 50 hives for the next mastery unlock, and you already have 48 kills on hives--the third hive you kill in your next game will not count until you go back to the Liber de Monstrorvm and claim the next mastery unlock.
So this is a minor example, but sometimes I forget to claim my mastery unlocks in the Monstrorvm which leads to an extreme example:
So an extreme example would be if you were to kill a cumulative of 100 Armored through various games but the mastery unlock was at 10 Armored kills--only the 10 kills would count towards the mastery and the other 90 kills would not be applied "retroactively" (I say retroactively, but it should be programmed to happen actively).
This may be a minor inconvenience because I guess you're supposed to check the Monstrorvm after every game, but I feel it is a needless inconvenience and wastes people's time if they are trying to farm those mastery unlocks. I can't think of why this would be a purposeful implementation other than to hinder the the speed of acquiring Blood Bonds, but honestly the amount of Blood Bonds you get from the Monstrorvm is negligible (I would advocate for a little more Blood Bonds because 15 Blood Bonds is pretty pathetic amount for how many kills are needed for full mastery but I digress).
Tl;dr: Liber de Monstrorvm doesn't carry over kills to the next mastery unlock when you kill more than required amount for the current mastery unlock progress you are in. A pretty needless inconvenience.
Edit: I have tested this and it is true that kills do not carry over onto the next page of the Monstrorvm. Below is my video testing this.