I have a Sony A6000 which I am trying to get working.

Problem is with these commands:
gphoto2 --capture-image-and-download --interval=-1
then:
kill -SIGUSR1 74577
(pid of gphoto2)
Sometimes it will work for 1-5 shots, but at some point it will result in a:

*** Error ***
PTP I/O Error

I tried running:
env LANG=C gphoto2 --debug --debug-logfile=my-logfile.txt --capture-image-and-download --interval=-1
but the resulting output file my-logfile.txt is 1.14GB, not sure why that is. I headed the first thousand lines of that file into a separate txt file (much smaller) to attach here.
manual-logfile.txt

For the issue itself (PTP I/O Error) I have found that doing this instead:
gphoto2 --wait-event-and-download
then a script file:

#!/bin/sh
# shootnow.sh - stop the wait-event-and-download (if it exists),
# shoot a new image now, and create a new wait-event

pkill -INT gphoto2
sleep 0.1                # avoid the PTP ownership error
gphoto2 --capture-image-and-download
gphoto2 --wait-event-and-download

will work and is much more stable than the SIGUSR1 method, so you might want to introduce a 0.1s sleep (or some other confirmation the pid has been killed) into whatever the -SIGUSR1 signal does in gphoto2?

I still need to find a way to make sure the original pid isn't currently downloading an image before killing it, because that results in the camera's ram filling up with a few shots then freezing.