IIRC, nohup has a number of weird and interesting quirks, and it generally doesn't do what people think it does
. (By which I mean, emulating daemon() in shell takes quite a bit more effort than that).
This might be doubly true for the ancient version shipped in Kobo's busybox version.
bb's up to date source (
https://git.busybox.net/busybox/tree/coreutils/nohup.c) helpfully points out an example which definitely sends it to bg, which is what I naively assumed you were doing (or launching it via something that effectively meant the same thing in practice).
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That said, I still wouldn't recommend sending any kind of long-running script's output to disk, especially somewhere under /mnt/sd or /mnt/onboard, as that can and will go down during an USBMS session.
(Note that HOME is stupidly / in Kobo's ash, which is also very much not great).