Maybe I'm missing something basic but I've been using Voyager with the Mark posts as read on scroll and Show hide posts button. While browsing the Voyager community, I scrolled till 19d mark and pressed hide posts. No matter what I do know, I'm unable to bring back those old posts. Shouldn't it show everything by default and only on pressing the button hide read posts?
As of right now, the button is just a toggle that will turn on the feature to hide read posts in your feed, but won't restore hidden posts (as you found). If you want to see your hidden posts, you can go to your profile (center button on the bottom buttons) and you can unhide a given post from the post itself.