This is a known issue affecting a few people which we've regrettably been unable to fix within the app (although our developers are continuing to try to find a solution with a big platform upgrade) - it seems to be a phone environment issue. Thankfully it can be resolved through a simple app reset! :)
Please follow these steps to resolve:
PREPARE
A) Go to Menu > Account and make sure that you're logged into a backup account
>> You may need to register because the backup account is an optional app feature not automatically linked with your subscription
B) Go to Menu > Account > Password & encryption key and reset your encryption key - make a careful note of it
>> All of your data will remain safely in the app during this process
C) Go to Menu > Database > Export and export an RYB file (save it to your iCloud files / Google Drive)
>> If you have photos in the app then also export these as a .ZIP file
RESET
iPhone: Delete, reinstall and reopen the app
Android: Clear your Read Your Body app cache and data in your phone system settings
RESTORE
A) Log into your backup account to restore your data
OR
B) Tap 'Get started' to navigate through the welcome flow as a new user then once inside the app import your RYB file at Menu > Database > Import
>> If you had photos in the app then also import these as a .ZIP file
Your chart screen should now load smoothly again :)
If it doesn't then please contact us for further support!