The moo-draw-blueline brush preset works in version 5.1.5 (which I just happen to have available).
It paints in low opacity white when used with version 5.2.2 and with a recent 5.3.0-prealpha.
The intended painting colour is set by the Colour: Hue curve which is flat at hue = blue.
That has stopped working for some reason.
It would be a good idea to file a formal bug report as described here:
Report a Bug | Krita
Attach the moo-draw-blueline.kpp file that you can quickly download from here:
moo-draw-blueline.kpp
When you’ve done that, please post a link to the bug report in a reply here.