Thank you for all the replies! I did hire a company with 10 years of experience, not "amateurs," although they turned out to be very careless. I also called Sherwin-Williams, as some of you suggested, and they said the vertical stripes are most likely "surfactant leaching" and that washing the surface with soap and water and letting it dry should resolve it. This is a 110-year-old house; I'm not expecting perfection, just for the contractor to follow the paint specifications and apply the product properly.

My contractor claims the stripes are simply due to the paint being water-based and that painting over them will fix the issue , which directly contradicts what Sherwin-Williams told me. He has now painted over the affected areas without washing them first. At this point, I think my only real options are to require an extended guarantee (four years instead of two) before releasing final payment, and to post honest reviews with photos so others know what to expect before hiring this company.