@goodie-bag I mean everyone started reading this for the comedy, it was a comedy series. As others have been saying the change happened because of the magazine the series was released in went under, so the author decided to wrap up the series in a big bang sort of way. These last couple chapters
were not supposed to have any kind of comedy. That's the entire point. There's nothing really confusing there in my opinion.
I think the transition was fine. The pevious chapter ended on her moving the train, this chapter jumps back to how we got there. It might not work well for TV but it works fine for a manga. Especially because we know the author had a very limited number of chapters to wrap up the series before the magazine officially closed completely. It mainly sounds like you're not aware of the MAJOR time constraints the author had. So it's less of a problem with the series and more just the author working with what few chapters he was allowed to do.
Your tunnel collapsing comment sounds like a nitpick in my opinion. We saw numerous times that the tunnel was still dropping some rocks on Torako that she was shrugging off. The people on the outside saw that the outside of the tunnel was caving in a bit, and you can apply that news comment to any time rocks were falling on Torako. This is a very basic method of conveying tension that hundreds of disaster movies use, it's not confusing and is a simple matter of connecting the dots.
Maybe you're not happy with the series and how it's ending, that's fine. However I think you could be a little bit less harsh given the circumstances, plus I'm just glad we got the series at all and that the author is going out with some kind of crazy bang despite the unfortunate IRL circumstances. (Edit: Changed this last bit and a couple of things some because I realized it came off harsher than my intent, and goodie-bag informed they weren't dumping on the series. My entire post probably needs to be updated and refined to reflect my original intent of wanting to converse and debate in a friendly manner. However I should probably leave the rest of it as is to reflect for future conversations and for context.)