Hi, I had this too, when you switch to text mode terminal, trying to login there, the X login screen takes the focus back after a few seconds, at least that is what I understand about how you describe it
Also /dev/sda2 is the raw encrypted LUKS partition, so after decryption succeeded you should not mount that one, but:
something like: sudo mount /dev/mapper/SolusSystem-Root /target
(from LVM system)
and probably: sudo mount /dev/sda1 /target/boot
that depends of course on how your disk partitions are chosen
For the first login problem I choose to rename /usr/bin/X to /usr/bin/Y, so that X was not getting in the way when trying logging in... (of course there are other methods) (I did that via Solus usb rescue boot) after that, reboot in normal system, then I could login in text mode, and update or change what I wanted... (when everything was working better, change Y to X again ;-)
O yes, I forgot, rename a file there is done like: sudo mv /usr/bin/X /usr/bin/Y