Hello itforsenior

It appears that after a certain number of lines or posts the topic
will move to a second screen page, and so on.

By clicking 'all' the view will change to show all posts of a topic
on a single screen page. This can be handy when a topic covers a
few pages.

However, the system prevents a single page when the topic is huge.
For example:

https://www.outdoorking-forum.com.au/forum/ubbthreads.php/topics/47929/1.html

Hope this helps.
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Jack