Comment 20 for bug 2017846

I do see the behavior you are describing in those logs:

Apr 27 00:34:53 Y4M1-II systemd-logind[2855]: Power key pressed short.
Apr 27 00:34:53 Y4M1-II systemd-logind[2855]: The system will suspend now!
Apr 27 00:35:10 Y4M1-II systemd-logind[2855]: Operation 'sleep' finished.
Apr 27 00:35:45 Y4M1-II systemd-logind[2855]: Power key pressed short.
Apr 27 00:35:45 Y4M1-II systemd-logind[2855]: The system will suspend now!
Apr 27 00:36:02 Y4M1-II systemd-logind[2855]: Operation 'sleep' finished.
Apr 27 00:40:00 Y4M1-II systemd-logind[2855]: Power key pressed short.
Apr 27 00:40:00 Y4M1-II systemd-logind[2855]: The system will suspend now!
Apr 27 00:40:17 Y4M1-II systemd-logind[2855]: Operation 'sleep' finished.
Apr 27 00:50:15 Y4M1-II systemd-logind[2855]: The system will power off now!
Apr 27 00:50:15 Y4M1-II systemd-logind[2855]: System is powering down.

Each gap is 17 seconds, which is interesting I guess.

If you are using suspend-then-hibernate (/etc/systemd/sleep.conf) and your battery is low, the system might be waking up from suspend to then hibernate (it does not look like you are on batter power though). Otherwise there might be a timer unit installed with WakeSystem=true that happens to be firing when you suspend. Besides that I don't think systemd would do anything else to wake the system (I don't see any other relevant uses of CLOCK_BOOTTIME_ALARM). If you want to investigate systemd involvement further, than you can enable debug logs for systemd-logind and attach updated logs if this issue occurs again.

$ cat > /etc/systemd/system/systemd-logind.service.d/debug-logs.conf << EOF
[Service]
Environment=SYSTEMD_LOG_LEVEL=debug
EOF

Probably best to reboot for that to take effect.