I think I solved my own problem. I found this:
www.nonumber.nl/news/blog/242-plugin-order-is-important
The article explains that the best ordering for your system plugins is:
- Any other plugins
- SEO and SEF plugins
- Cache plugins
So with my order change to place Disqus as the last plugin was a clear mistake, and I updated the Disqus order field to Allvideos (so it is processed after Allvideos). The result - article titles are shown, the Allvideo videos are redered, and Disqus comments are also working.
While I do not have a way to identify SEO/SEF plugins from cache plugins, I can say that the plugins for application features should be placed higher in the order.
I hope this helps others.