no? her sickness has been acting up continuously throughout the series so far with multiple situations - she is probably simply nearing her limit right now.
what happened during that boat arc then??
what about it? she was born with a weak heart and all we know is she's fragile and has "fits" where she gets extremely sick - and that she's most likely going to die very young. her illness doesn't disappear just because a situation you think should trigger it doesn't? even in ch 1-7 a lot of "action" - as you call it - happens, yet it's first in ch 8 she coughs up blood and gets bedridden. she has a permanent condition that is worsening constantly. it's not pick and choose when it hits her.
thinking the author "randomly forgets" a key part of the mc and the story in 24 chapters is a bit of a stretch, don't you think? especially when it's brought up so many times and we see flashbacks of it consistently? having it happen in ch 8 and then ch 24 makes perfect sense considering it's an unpredictable disease while not much time has actually gone by.
wait wait wait
so much action happened so far, but her sickness acted up now? does the author randomly forget that she's sick?