It seems that synchronising the data does no longer work when using the application on different platforms and storing the data on OneDrive. I can change data on any device, however, the changes do not show on a device running on a different platform. Synchronisation between iOS devices seems to work, likewise the data on W10 devices shows as expected.
The iOS app version is 6.0.6 (234), the W10 app version is 5.5.7.