Udisha
Food scraps
This one is probably obvious. Small scraps of food like bits of vegetables, meat or cartilage don't dissolve while the dishes get washed. Instead, they get stuck to the dishwasher filter where they rot.
Glass and ceramic shards
Hidden shards of glass and ceramic may get chipped and stick to the net, damaging the mesh by tearing it.
Mineral deposits
If the water used in the dishwasher is iron heavy or hard, minerals or granules can get trapped as they continue to get collected at the bottom.
Adhesive labels
Stickers or price tags on new dishes are often overlooked and while the the paper material gets dissolved, the adhesive usually clings to the mesh, eventually blocking drainage.
Solution
While it is very difficult to meticulously check for deposits in the filter often invisible to the naked eye, the best way to make sure that the filter is clean and unharmed, is to clean it regularly.