Why does my glossy photo paper have vertical creases?

Are you running it through a top-feed or bottom-feed printer? I’ve seen that before on multiple bottom-load Epsons with mid-weight photo paper. Even 65-lb cardstock will do it, so it's a mechanism flaw on bottom-feed units. There is no fix; it's a limitation of the machine.

To avoid that, you really need a machine with both a top and bottom feed for heavy to mid-weight photo paper, as the top feed doesn’t crease photo paper like a bottom feeder will.

This is why true “photo printers” (ESPECIALLY the ones with photo grade color sets) have both, or are top only. Epson has moved to having both on a lot of the newer photo grade units, especially the ET-8500/8550 generation where you have trays for mid weight paper, and a top feed for rigid stocks - the 8550 even supports 13x19 posterboard in it's top feeder, so that gives you an idea what they can do with that configuration and heavy papers. Even the ET-15000 and the EcoTank Pro lineup is going hybrid. Any of these bottom feeders are either a few years old or were always cheap affairs from when they were new. Any of the more current "Claria HD" cartridge based machines even went hybid - Epson used to do one or the other for years, but they offered both on anything respectable for a few years.