Hey, I've been working in the book industry for 32 years and can give you some insights into what is probably going on.
Penguin Books, the publisher, has run out of copies. There is a huge paper shortage in the US right now, cause by Corona and Trumps trade deals, which is making it much harder to physically print things right now. My guess would be that Amazon ran out of copies, reordered from Penguin, and Penguin doesn't have any more, and has decided to delay a bit to allocate their supplies of paper to other new books before doing a second print run of Peace Talks.
Depending on where you are in the United States, if you have an independent bookstore near you, I would recommend going to them. Most Indies order from a distributor called Ingram Books, and they still have copies left in most of their US warehouses. If you go there they could order you a copy and have it within a couple of days.
Otherwise, I would guess you're out of luck till October.
Amazon cuts their profits so fine, that the 5 or so % difference in their cost from ordering from Ingram vs direct from Penguin would make them unable to ever order from them, but Indies can't operate that way, so they would be happy to do it for you.
Edit- Though Amazon currently says they have it in stock, so not sure what the heck is going on there...
Edit again - Now when I checked Penguin again, it is listed as back in stock. Probably why you guys got notifications that you are getting it after all.