I uninstalled and reinstalled the app. After a quick test, I'm now able to save and load layouts I've created. But I'm not able to import a layout. When opening the layout file for coolquentin's OP-Z layout in iOS's Files app, I choose the "Copy to MIDI Designer" option, and then it says, "Problem restoring, rolling back." I get the same result when opening a layout I created before the reinstall. At first, it gave me the option to append or not, and I tried both, but the layout was nowhere to be found. Now, I only get the "problem restoring" message.
After uninstalling and re-installing again, I'm able to get the append or not option. When I say yes, I get the message, "All good, restored" but there's no effect on the current layout. When I say no, I get the "Problem restoring, rolling back" message.