We found the cause of this error and fixed it on v1.9 of the iOS PIE app. This version is currently being reviewed by Apple and should be available for update around August 30th. We will send out an official update as soon as the update is up on the App Store.
This error was caused by the fact that some countries use a comma(,) as the decimal separator. These countries include Belgium, Brazil, Denmark, Germany, Greece, Indonesia, Italy, Netherlands, Portugal, Romania, Russia, Slovenia, Sweden and more in Europe.
When you press the save button on PIE, PIE converts raw data from its sensor into a format that we can comprehend. This size data is then sent to your smartphone app. Until v1.8, PIE sent data in the 123.45 (period separator) format, which iPhones in the regions that use 123,45 (comma separator) format couldn't understand and hence displayed as 0.
The v1.9 of the iOS app, which will be available around August 30th, fixes this problem by following the standard used in your region.
If you think of yourself as an early adopter and are in the mood to test this out or just can't wait until the fixed update is ready, you can change the region settings on your iPhone or iPad to fix this issue temporarily.
On your Apple device, go to Settings > General > Language & Region > Region and select United States. It may take a few seconds to change the settings of your phone, but you will be able to return to your original region without any problem.