In chapter 18 (page 210 of the referenced scan below*), Mike is drunk and slurring his speech. Hemingway conveys this drunkenness with spaces in the middle of words: "I’m getting a lit tle sleep. I’ve want ed a lit tle sleep for a long time…I haven’t got ten to sleep yet…I’m just start ing. I’m go ing to get a lit tle sleep."
I understand the spaces are true to the original, but it reads to me more like a transcription error in the ebook than a stylistic choice by the author.
I suspect replacing the spaces with hyphens, per section 8.7.7.6 of the style manual, isn't the right choice since it would make the dialogue feel less broken and more rhythmic. Maybe a good compromise here would be hyphen + space? That would keep the speech broken while also making the typography more obviously intentional.
This could also just be a me thing and the spaces as they are might be fine ¯\_(ツ)_/¯
*: I'm not sure if this was the exact scan used in producing the ebook since the link in the colophon is broken, per the Issue I opened on the repo.
Reference:
https://archive.org/details/bwb_C0-BYG-464/page/210/mode/2up