I’ve been importing a lot of old pictures from my Flickr account and consistently keep getting 504 Gateway Time-out errors when importing more than just a handful at a time. This happens on different computers/networks, at least one of which is using high-speed internet access.
Despite the error, the import seems to go through ok and eventually will appear when I reload my observation list. Sometimes it can take a few minutes. At first I thought the import failed and went back to try again, which then resulted in duplicates I had to clean up, so just a heads-up to anyone trying the same.