While traversing the 1.17 terrain I came across multiple cobwebs in a mineshaft that seemed to emit light. After breaking them the light bug was gone. The mineshaft I was in overlapped with another one and a fortress was also there. Later I saw that its not only cobwebs but random block aswell.

Screenshots with F3 Screen where you can see the light level down below

This is my first bug report. I hope its good enough.