If you find that your Touch app won't unlock a door that previously could be unlocked, the first place you may want to check is the Permissions and your Credentials in the pdk io - People portion of the application.
Ensure that you still have permission to access the door you're trying to unlock. Also, ensure that the Touch io icon at the top right of the Touch app doesn't have a circle/slash over the icon (as in the following image), indicating that the reader is not currently functioning.
If it turns out that there is an issue with your Credentials or Permissions, you'll want to either correct them, update them, or delete your current credential and have a new credential issued to you.
The next area to check may be the door reader associated with the door you're unable to open. It may be that the reader or door hardware connected to the reader has malfunctioned or is not getting sufficient power or some other issue that prevents the door from opening as it should.
See also: What to do if your Touch App won't open.