Had a similar issue recently, turns out the galvo mirrors were dirty. Most of the parts I was printing turned out fine, but I had issues with small details and this “filling” of the gaps in between rafts. Ended up thoroughly cleaning the whole path of the laser (galvo, big mirror under the tank, optical window, tank’s underside) which solved the problem.
Since Formlabs seems to have issues with their support website this week-end, you might wanna print this by yourself :
If the number on the columns aren’t all clearly visible (it’s normal for the column to be a bit deformed, it’s part of the test), or if the features of the centerpiece are not well resolved then you might wanna first look into cleaning the tank and the optical window, then contact formlabs if nothing has changed.