WiFi can disconnect from time to time (in Linux). This is the most annoying problem with the X1C7. It vanishes for some days, before returning.
See reddit discussion; Looks to be this bug, though in 2021 I’m seeing more of the 0x707 bug.
As a workaround, I decided to use an external wifi card (AC600M USB WiFi Adapter) - but that also had its own connectivity problems from time to time.
Update (Sep 8,2021): This issue appears only on NixOS (as well as Ubuntu, and possibly several other distros), but not on Clear Linux.