When you have an encrypted volume, and you first boot up, you get the usual LUKS password prompt. However, whatever keys you type for the first second or two gets ignored. This just creates confusion and can result in needless IT inquiries. To make matters worse, it's not always the case that the password is displayed with * characters. Sometimes it's just blank. The real solution is to not display the prompt until the OS is ready to listen.
I actually doesn't ignore the first key strokes, it just takes a bit until it's ready. Wait a few seconds and all your key strokes are recognized. I also didn't have the case that it is completely blank when entering the password.
However you are correct regarding the fact that it shouldn't be displayed until it's ready.
Maybe related: If you have an NVidia GPU and use the proprietary driver, lightdm doesn't recognize the first keystrokes either. it only recognizes them from the second or third onwards. Weirdly enough, this doesn't happen on the Intel iGPU or on AMD GPUs.
So maybe it's just NVidia having an awful driver again.
Considering this happens before most of Solus has even begun to boot (hint: just the kernel and initramfs) this is most likely the result of BIOS/UEFI fighting with the KMS driver for your video card. Not sure that we can really fix this problem.