Started to use the hydration feature and changed one of the 'quick add' to 900ml to match my water bottle. However, the app keeps resetting this back to the standard 750ml.
OK I would try disconnecting your phone from GCM. The go into the web site and change your values. Press save on the web site, go straight to GCM on your phone and do a sync with the web. Then reconnect your phone and do another sync.