I had a customer with this same issue, but found a solution. There are a few key items needed to make this work. The simplest solution is to restore a pre-iOS 11 backup to another phone that has not been updated to 11. This should work.
Option 2 - items needed to pull this off
- You need a backup of your phone before the iOS 11 update. I'm assuming that the PW app is 32bit and that is why it doesn't work on iOS 11.
- A backup created from the PW app will be needed to restore.
- An iOS device that has not been updated to iOS 11.
Apps that are not available on the app store anymore, like PW, can be restored from a backup in iTunes.
Here is what I did to get the PW and its data recovered.
- Backed up the iOS 11 phone to iTunes. Backup to computer not cloud.
- Make sure the computer is authorized for purchases on the iTunes account the app was purchased from.
- If the PW app doesn't show up in the phone Summary after the backup, you may need to download all purchases.
- Once you are sure you have the app on the computer, plug in a non-iOS 11 phone and setup as a new phone. Install the PW app.
- Start up the app to verify it works. Go to Settings in the app and do a Backup - Recovery. Here it will tell you to use your browser and enter the IP address it shows in the app. On a Mac, use Firefox, Safari and Chrome wouldn't show the Choose button to select a file to restore from.
- Select the backup file from your PW app, assuming you have one, and restore.
That's what worked for me. Someone else may know a better solution. 