If you're pregnant, vaginal steaming can induce miscarriage. It can be problematic if you've got fibroids, and in certain women it can cause bacterial or fungal infections. Burns are also a huge issue, because it's very delicate tissue that can be really easily damaged.
There's no guarantee that random people on Instagram are giving good advice, and they aren't governed by anybody – unlike doctors.
I do think part of what's driving the wellness industry is women who are sick and have not been taken seriously by mainstream medicine, and have conditions that haven't been well researched.