Trying to explain the Chain Lightning finale in terms of Hypertime
here goes:
First, an explanation in line with the basic many-worlds approach to time: When Wally changed the past, he could only go forward again in the timeline he had just created. This makes perfect sense when Wally’s the one making the changes, but it doesn’t explain why Cobalt Blue killing Barry changed history around Wally. (Similar problems apply to stories like Bart Saves the Universe.)
So, a Hypertime-based explanation: The Kingdom #2 described Hypertime as branching off of a “central timeline” or “main timeline,” i.e. the mainstream DCU. Given that DC has a long, well, history of stories in which time travelers change history, perhaps what’s going on is a realignment of which timeline is the “main” timeline.
It’s not totally consistent, but then neither is any other explanation. Personally, I think the DCU is too big and too complicated to ever hope for 100% consistency. With 60 years of stories (some of which have been officially removed from canon), hundreds or thousands of writers, artists, and editors, it’s sometimes amazing it’s as consistent as it is.