On NixOS 25.05 (nixos-unstable branch), with Lockbook 0.9.16. I'm not sure how to debug this. Happy to help if you can give me some pointers.

(Actually, I experienced something similar with 0.9.15 as well, but I didn't open the issue since I was using Lockbook very little in the last few weeks.)

Note: I've always seen the Failed to get Xft.dpi messages, never been a problem. I don't think it's related.