To be honest I didn't search forum about it, because I have no idea how to search it. Basically a light group creating white curve lines
Which is group of a simple disk light (generate caustics unticked) :
It's a single plane, so no objects colliding either.
After 100 passes it doesn't look like a glitch, it's a result of something but I don't understand what cause it is :
Edit : Max 2023, Corona 8 hotfix 2