The Hide Sold Out app allows not only to hide 'sold out' products by making them unavailable for purchase at Online Store but also automatically unhide them when they are back in stock.
In case you have noticed certain products to be not published back when the inventory rises, please make sure to check if the 'Un-hide sold out items if inventory greater than 0' setting is enabled under the Hide Sold Out tab in the Power Tools admin:
One thing to keep in mind with the un-hide option is that the app will only un-hide products that it has hidden previously, it won’t un-hide any items that were manually hidden from the store by you (by making them not available for purchase in the Online Store).
This could be the reason that products aren’t being shown when the inventory is being updated.
Additionally, please note, that the app hides and unhides the items during the store update, which is usually being run every hour or so.
You might just need to wait for the next store update to be completed.
If you have any additional questions, please contact support through the live chat in the app, or at firstname.lastname@example.org