Without specifics, threads on this forum often end up as hypothetical situations. From your screenshot I believe I've figured out your Master Account, and am guessing at the actual project being used. We need as much information as possible when scanning through millions of log entries. I'm looking at a few things.
I would recommend you reach out to support and log a ticket right away if you want a quick solution. That allows us to prioritize the issue higher. They will also get information from you that helps figure out the problem and will ask for more access to your project.
It isn't that large of a publication, this is the 16th issue, and they have all been around the same size as far as number of articles and the size of each article. Last issue, which published in October, I had no issues at all. I uploaded the articles, preflighted and published. This go around, I uploaded the articles, and am unable to preflight them. I'll put the screen shot of the error I'm getting, i've tried different browsers as well as different computers.
I also noticed that the publish/unpublish buttons are grayed out, even on previous articles/collections.
I've asked my client to look on their end to see if the user roles have changed; but again they shouldn't have because as far as i know nothing has changed between October and now.
Can you tell us what you've tried so far? What platforms you have tried to preview it from (device? browser?)? What network speeds are you experiencing? It is a large publication? I assume this worked fine up until now? What was changed/updated in the publication before this started happening? What is the exact message that it is presenting you?
If you call support and get a ticket open, they'll get publication information from you and a more in depth investigation could happen.