This is usually to do with a sync not running through properly. Items created after the sync date will still come through but the sync will not register the older items, assuming they are already synced.
To resolve this, we need to select the paper and cog icon and tap Cropping History to Sync-
Change the amount of years of data held on the device to None and tap Settings and then Cancel -
This will run a sync through and, once it's finished, go back to the Cropping History to Sync.
Change the selection back to the original (or higher if the plans/crops are missing that are outside of that date range).
Another Sync will run through and will likely bring the missing data down to the device with it.
If this does not work, uninstall and reinstall the app (Search 'GLGM' in the app store).
This will bring a fresh load of data to the device as well.
If you are still having issues, please get in touch with support through firstname.lastname@example.org.