"Crazing" is small cracks you get on the surface.
It is caused by buildup of internal stress in the acrylic, especially around cuts and openings. Over time, especially with UV light,
these stresses can cause lots of tiny cracks at the surface.
A solvent, including acrylic glue like #4, can really trigger the formation, since it loosens the polymer bonds.
While a bit ugly, micro-cracks are not usually a problem.
If you want to see it, take an only piece of acrylic, and dip in lacquer thinner. Should show up on the edges.
The complex way to reduce that is "Annealing".
Where you heat the acrylic to about 180 degrees, and slowly cool. Eliminates the internal stresses.
I have heard of people using boiling water in a big tub for several hours.
Another idea is to use weld on #40, and glue pieces above/below the area of concern.
Since that is more resin, less solvent, supposedly less likely to craze when used.