Follow up on my last comment: I can reproduce the issue and I think it's related to the audio subsystem.
I can suspend/resume if the "Cannon Point-LP High Definition Audio Controller" is set to its "Disabled" profile in pavucontrol (which means my speakers/mic/headphones aren't working). If I set it to "Play HiFi quality Music (unavailable)", the audio is working but I can't get out of suspend mode.
Some people are experiencing the same issues on this specific laptop: https://bugzilla.redhat.com/show_bug.cgi?id=1772498
Fedora 31 with latest updates + 5.5.5-200.fc31, can't resume from sleep (had the same issue with Linux 5.3.x kernels). I'm not even sure it reaches S3 as my laptop spent the whole day draining its battery and keeping itself warm. Will do further testing to check if this issue can be reproduced easily and diagnose its origin.
This said, my mic is now functionnal under Linux thanks to Linux 5.5.
Hardware: Lenovo X1 Carbon 7th gen with 8th gen Intel CPU, no external peripherals, no LTE card, Bluetooth disabled in UEFI.