Ah yes, I had this issue once, sadly I think you need to buy the Vol.2 of the magazine because its taking priority from the Mabel´s questline, when i had the issue i try to go back a few saves but it was the same, so my solution would be that, to buy the magazine, money don't tend to be a problem if you passively produce money via harvesting or selling the bottles of milk, and once that´s done you´re good to go, even tho, sometimes the Cheat phone can help you too, i believe one or two quests suggest you to use the cheat menu to advance, Aunt Douie does it so yeah, hope it helps