Recently, on my iPad, whenever I tap on SkyDemon Plate under airfield, the button turns blue for a while, however, nothing happens. No Plate is shown. The same is true for Textual Information button or any other Ground and Visual Approach maps. The other buttons (Approach Information, Admin, Information and Fees, Fuel, Facilities) work ok. Also, for the maps that have a "point on map" icon, the map shows up overlaid on the map. And, when I zoom really close on the map, the map of the airfield shows up (the same map that used to open with SkyDemon Plate). None of these show up on their own when pressing the button. I am using iPad 7 with iPad OS 14.6 and the latest version of SkyDemon. 

It's not an issue known to me, but it sounds like the built-in PDF viewer is not working for you. I do not know what could cause that to happen because it's part of the iOS operating system.