Hm... Ashley's max level is 40, so you seem to be missing a few events there. I can't remember how many relationship levels you get in the last event, but I don't think it's 4.
Did you use any cheats? Cheating friendship levels can and *will* come back to bite you, unless you know *exactly* what you are doing. And by that I pretty much mean "unless you are Runey", or at least acting under advice from Runey to fix a bug.
Otherwise, all I can think of is: did you get all the college events *and* the bar events for all of them?
Also, you might need the barista outfit for Maria as well.
Anything more than that I think needs Runey's attention.
(Edit: thinking about it, the cheat option is the most likely to have broken stuff, so I moved it up for readabilty)
I managed to get Ashley's birthday last event to trigger by using the max stat code on the twins, Maria, and the Android but was greeted by a recurring warning message so I'm going to say that is what you were referring to.
I hadn't used any codes before but having played around now with changing stats and friendship levels, I'm wondering if there are codes to reverse them, so you could say reset the friendship level or move it to a certain spot? I noticed you can do this indefinately with Nia and Sylvia, and this would be a great way to go back and run through things again on certain characters without actually restarting.
I believe there is a Patreon level that gives you access to the nuclear football, which I so dubbed because it has a good chance of nuking your save by setting friendship levels independently, to whatever index you want, with essentially no restriction (AFAIK).
The problem is that the game is complex. Like, MB upon MB of lines of code complex. There are interlocks in the girls' stories that can end up with a situation like the one you had, inconsistent states that make the game unplayable.
The "max-this" cheats are safe, because Runey specifically went to the trouble of making them safe: they cross-check that all the interlocked states are appropriately updated, so that, like in this case, if you are maxed with the twins you are also at the minimum required friendship with ashley. They also set whichever hidden variables need to be set to their appropriate values.
Going backward is a lot more complicated: even something as simple as setting all friendships to 0 isn't guaranteed to work, because there are other variables that have been set and need to be reset. The game does not expect you to see *unique* events *twice*, and so inevitably all those states are not meant to be updated twice, which, again, can leave your save in an inconsistent and unplayable state.
In better news, most events are replayable in the gallery, and you can even make different choices and see how they would have played out. These choices don't affect your save, for better or for worse, so you can go crazy.
