This seems to happen at night time. Nothing on the tomatoes themselves. Sometimes it looks like small white gnats fly off the plant when I inspect it. Have not found any aphids or spider mites. Bottom of leaves look clean.
Tomato Leaves Have White Wiggly Lines
Certified GKH Gardening Expert
Are you notincing any yellowing of the leaves or other symptoms (i.e. holes)? It could indicate leaf miners, which often leave squiggly lines throughout the leaves. Here is more information: https://www.gardeningknowhow.com/plant-problems/pests/insects/leaf-miner-control.htm
Since you mention this seems to happen nightly, it could also be the result of slugs or even snails. They commonly leaves white or silvery colored "snail trail" wherever they have been. They would also feast on the foliage. Here is more info on these pests: https://www.gardeningknowhow.com/plant-problems/pests/facts-about-slugs-and-how-to-kill-garden-slugs.htm
It may be helpful to spray the plants with neem oil. This is generally effective on many types of insect pests and is also a fungicide, should any other issues pop up as a result of the pests. This article will provide additional information: https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm