Eduard Metzger Yes, it's on consistent on every note. I'm having to remove horizontal rules from older notes, just to see them. And I've rebooted my Mac too since the issue started (since, again, it started when I installed 13.10.0, so a while ago now). I'm on macOS 10.14.6, on a 2015 MBP (and the issue behaves the same whether I activate the integrated GPU or the discrete GPU). Perhaps it's an issue only on older macOS's?
Gem Oh, ok, macOS Mojave is pretty old. That's most certainly the issue. Maybe not the GPU, but you would have to upgrade your macOS if possible. It's hard to test and provide compatibility with older OSs as Apple deprecates features and introduces new ones in new OSs, making the code a mess.
Eduard Metzger It's alright thank you for continuing to support it in at least partial capacity. I can't do without 32-bit support, and I don't even like the UX of modern macOS versions, but I can do without horizontal rules.
Thanks for sharing this! It seems work for me. Might there be something else going on? Can you reproduce it with every note?