During the night the screen is still too bright, so I added the gamma option, like this:

wlsunset -l 1 -L 1 -g 0.5, which looks very nice.

Only to notice that that gamma is also applied during the daytime. Of course, I can set the low temperature too, so this is not a bit problem, I thought it worth mentioning.

Does not happen any more.

wlsunset runs fine until the failed message after which the gamma is returned to the daylight default.

setting temperature on output '47' to 4689 K
setting temperature on output '47' to 4665 K
gamma control of output 47 failed
setting temperature on output '47' to 4641 K

I've even created a script to automatically restarts wlsunset after it stopped working:

#!/bin/sh
while wlsunset -l 46.8 -L 8.5 2>&1| read line; do
    echo "$line" |grep -q failed && pkill wlsunset
done

This problem also happens with redshift. This problem also happens if I change to another location.

I think it's because I logged on and off a few times. Does wlsunset die with the sway session? If it remains running we have the cause of our problem.

At a few minutes before 11:00 wlsunset went crazy. Before killing it I straced the process and got lots of these lines:

sendmsg(5, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="\6\0\0\0\0\0\10\0", iov_len=8}], msg_iovlen=1, msg_control=[{cmsg_len=20, cmsg_level=SOL_SOCKET, cmsg_type=SCM_RIGHTS, cmsg_data=[7]}], msg_controllen=20, msg_flags=0}, MSG_DONTWAIT|MSG_NOSIGNAL) = -1 EPIPE (Broken pipe)
poll([{fd=5, events=POLLOUT}], 1, -1)   = 1 ([{fd=5, revents=POLLOUT|POLLHUP}])