I was also frustrated 😤 during the time I applied for verification before.. I sent messages to support many times coz I wonder why its always error and coul even see the button for uploading photos until I asked someone's help and he told me to click desktop site coz I'm using phone. and that's it I able to submit successfully and get verified. If u are using phone try to use desktop site so u can see all clearly..
I used my phone before and it works well for me, try to use google chrome but if still not happen there is something wrong with Poloniex. Ive heard the news about this case and I think this problem is already on the legal court, maybe you can search more about this and wait for the result of this case.