If anyone was wondering where all our old topics went:
Good news! They were still here. Just hiding.
There is a setting in the control panel where it allows us to show topics and posts up until a certain date (like 'last 90 days'), I've just corrected it to "Show All".
And just so everyone knows, if I (or anyone else) makes a brand new section, and forgets to click 'Show All', there are drop-menus at the bottom of all sections that will allow you to see posts.