I made a playthrough squarely focused on corrupting Holly to test the inconsistencies in Holly's paths and things don't make sense. The corruption included Ian sleeping with her, Lena encouraging her to go for Mark, Marcel, and Stan, kissing her as Lena, and getting all the stray holly_change variables.
This route had Ian open up to her, it seems on this path they are moving forward with their relationship, but Holly seems bugged by something.
I think this is because of her attraction to Lena, later she automatically kisses Lena and cries about it. It can't be about cheating on Ian with Mark because at this point it hasn't happened and Lena can techically prevent her from going in a choice later. Wouldn't make sense for her to regret something that she might not have done. You could argue that she is tense because she is considering cheating on Ian with Mark, but that also doesn't make sense because earlier says she isn't interested and my Lena was the one to blow him in chapter 10.
Later at Lena's parents' house Lena and Holly discuss Ian and Holly confronting him about Gillian. This scene takes place before the screenshots posted above. Right after they shift the conversation to being about Mark and Lena can encourage her to go him. Keep in mind this timeline:
Friday
First sex scene of chapter 11 with Holly and Ian
Gillian is spotted
Saturday
Ian is at the art gallery
Lena is at her parents house, encourages Holly to go on a date with Mark
Sunday
Afternoon Holly and Mark date
Ian and Lena evening sex
Monday
Ivy spills the beans on Mark and Holly
Tuesday
Holly visits Lena
I know its technically possible for Holly to have gone on a date with Mark, slept with him several times, shown up to Ian's and slept with him aswell in the evening. BUT it is highly unlikely considering there is no indication from her and she must have some stamina if she can go at it +4 times in a day with two different dudes.
Another inconsistency is this line from Ivy:
She has literally heard Holly talk about sex with Ian and how good it is in previous chapters. Furthermore, even in this chapter she is talking about how good she heard it is:
This screenshot is her on Tuesday talking about how Holly gets good sex from Ian, but the day before she was saying Holly hasn't gotten any good dick?
The final inconsistency is Lena. Lena on this path has been attracted to Holly and way back kissed her at Ivy's place. Now on Tuesday Holly kisses Lena and instantly starts crying about it. Lena lectures Holly saying it shouldn't happen again and it was partially her own fault. If Lena sees her kissing Holly once as interfering with Holly and Ian's relationship, then why wouldn't she see Mark as fucking her 'several times' as also interfering with their relationship????? Same with Holly, how are you going to burst down crying cheating with Lena, but have the resolve to cheat with Mark and have sex multiple times? It just doesn't add up.
TLDR: Holly cheating with Mark is either horribly handled or wasn't intended to be added.