Thank you for following up @George Drake!
In this case, could you please try importing your document and extracting its pages in a private or incognito window to help us narrow down the potential cause? Did you indeed try connecting to a different network, such as mobile one, or disconnecting from your VPN (if applicable)? Sometimes account performance issues can be related to internet security/speed or browser issues. These steps will help us eliminate that possibility. For help with opening an incognito window, please see this community post.
If those don’t resolve the problem, can you please send a screenshot of the associated Javascript Console output after reproducing the issue? You can open your Javascript Console by pressing Ctrl+Shift+J (if your computer is a Windows/Linux) OR Cmd+Opt+J (if your computer is a Mac).
Once again, we appreciate your help and patience!