Using testing repo, having the following versions of what I guess is related:
extra/gnome-settings-daemon 3.20.1+8+g40bf4fd-1 (gnome) [installed]
extra/gnome-shell 3.20.4-1 (gnome) [installed]
extra/gnome-shell-extensions 3.20.1-1 (gnome) [installed]
testing/cups 2.2.0-2 [installed]
testing/libcups 2.2.0-2 [installed]
extra/cups 2.1.4-2 [installed: 2.2.0-2]
extra/cups-filters 1.11.3-1 [installed]
extra/cups-pk-helper 0.2.6-1 [installed]
extra/libcups 2.1.4-2 [installed: 2.2.0-2]

Every time I log in to my gnome, gnome-settings-daemon uses 100% CPU. I tried disabling GDM and replacing it with lightdm, but it didn't change anything.

I think it's related to cups because of the following backtrace, but stopping cups services didn't help.

# gdb -p $(pidof gnome-settings-daemon)
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Attaching to process 1244
[New LWP 1249]
[New LWP 1251]
[New LWP 1252]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/usr/lib/libthread_db.so.1".
0x00007fef0d8fe98a in setsockopt () from /usr/lib/libc.so.6
(gdb) bt
#0 0x00007fef0d8fe98a in setsockopt () from /usr/lib/libc.so.6
#1 0x00007feee8d00a26 in httpAddrConnect2 () from /usr/lib/libcups.so.2
#2 0x00007feee8cff3be in httpReconnect2 () from /usr/lib/libcups.so.2
#3 0x00007feee8d2493f in cupsSendRequest () from /usr/lib/libcups.so.2
#4 0x00007feee8d24d54 in cupsDoIORequest () from /usr/lib/libcups.so.2
#5 0x00007feee8cf149b in _cupsGetDests () from /usr/lib/libcups.so.2
#6 0x00007feee8cf263f in cupsGetDests2 () from /usr/lib/libcups.so.2
#7 0x00007feee8f55ccd in ?? () from /usr/lib/gnome-settings-daemon-3.0/libprint-notifications.so
#8 0x00007fef0de19d1a in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#9 0x00007fef0de1a0d0 in ?? () from /usr/lib/libglib-2.0.so.0
#10 0x00007fef0de1a3f2 in g_main_loop_run () from /usr/lib/libglib-2.0.so.0
#11 0x00007fef0ebafa65 in gtk_main () from /usr/lib/libgtk-3.so.0
#12 0x0000000000403780 in main ()
(gdb)