Progress with all characters is based on a combination of relationship score and previous steps. That's why simply cheating the relationship scores breaks progression and bugs out the game.
Thanks for clarifying this. Unfortunately the Walkthrough doesn't give a warning about this. Therefore I guessed that increasing/decreasing the Relation Scores shouldn't have a game breaking effect.
I raised the Relation Scores at least at the beginning, but only moderately (usually in steps between 10 to 30 score points), because I wanted to skip over the redoing requirement of the same steps to the next given threshold of that character according to the Walkthrough. And I didn't encounter any issues there - until it came to Kira and partially Adrianna.
The possibility to do the Emma Massage steps appear already when Adrianna is still at Relation Score 175. Therefore I tried to do them right at this time. And I was able to do all the predecessing steps until it came to sending the message to Adrianna that Jason was now ready to do the massage together with her and she would suggest to go to Emma at 18:00.
At this time I had Emma at about Relation Score 360 to 380 and Kendra had not shown up.
Probably Rebecca's Relation Scores have an impact there, too, especially when it comes to Kira and the math test trigger.
However, it wasn't difficult to get her up to Relation Score 300 and the Walkthrough did that quite early when Kira wasn't even mentioned.
The requirement for Julia to have another girl to do a photoshoot appears quite early in the Walkthrough at Step 153.
I postponed that and managed to raise Julia's Relation Score up to 360 to 380 by loosely following the Walkthrough.
It's true that I did the steps for characters I liked (like Rebecca and Adrianna for example) somewhat earlier than suggested in the Walkthrough, but I didn't simply raise their Relation Score to the maximum because I wanted to do that step by step.
When I reached a dead end because predecessing steps for other characters were required, I tried to catch up with them which usually wasn't an issue at all. That's the how I was able to reach the nearly maximum Relation Scores for the other Characters.
But even when Emma reached Relation Score 450 the possibility to message Adrianna because of the Massage session wasn't triggered. Because I wanted to assure that I just didn't recognize that I already sent the message to her, I went to Emma's house at each day of the week at 18:00. However, Adrianna never showed up.
Additionally I reached the point when it was necessary to finally do the required steps for Kira. I had her already at Relation Score 10 because of the school key requirement. But for some reason the math test steps didn't get triggered for weeks. Only the trigger to ask her to do the photoshoot with Julia showed up. That's the reason why I raised finally her Relation Scores first to 40, then 80, 100 and finally to the maximum.
That was the point where I recognized that some of the steps for Kira were triggered by her Relation Score level (which btw. is a bad idea at all) and some not.
Additionally the trigger for Adrianna to offer the cheerleader outfit was never initiated despite fulfilling all mentioned requirements according to the Walkthrough. That was the reason why I finally first raised Adrianna's Relation Score from 175 to 225 and then later to 260 to see if both mentioned steps would get triggered then. But they still don't get triggered.
That is the reason why I have the impression that there might be some accidently created trigger windows for those steps that also get closed at some point. And exactly that shouldn't happen.
Additionally I suggest that all successive steps should only be triggered when all required predecessing steps have been completed but never only when a certain Relation Score threshold is met. Relation Score thresholds can be an additional trigger but they never should be the only one. This way it can be ensured that cheating the Relation Scores to have a fast track through the game doesn't break it.
I also strongly suggest that there should be a warning added to the Walkthrough to NOT to use the cheating menu to raise Relation Scores as this might break the game.
I'm starting a new game now by exactly following the Walkthrough though I think that Walkthroughs shouldn't be the only successful way to play such a game.
And I have to admit that somewhat bothers me that I can't even cheat a little bit in order to avoid dumb redoing of the same steps over and over again if I don't want to risk breaking the game. I personally don't believe that in this case there should be a cheating menu in the game at all.