By skyforbes I ran into the dreaded download link failure on ChatGPT last night and this morning I was able to get around it and fix it by switch models. I was using 5.1 and switching back to model 4 and regenerating the prompt it instantly created the PDF file for me to be able to download.
Maybe it only works for me, but after searching for a bit and trying other ideas this one worked for me so I thought I would share with others.