In case you have made a backup of your device before the update, here is the solution how to restore your data. Otherwise this little tip can not help to recover the favorites, sorry.
Restore TomTom Favorites
To restore your favorites, just find the backup folder, which on my computer with my German version of the software is
C:\Users\<<YOUR USERNAME>>\Documents\TomTom\HOME\Sicherungskopie\ONE XL\Backup01
or in earlier versions was
C:\Users\<<YOUR USERNAME>>\Documents\TomTom\HOME\Backup\ONE XL\Backup01
In there you should find a directory named \InternalMemory\Western_Europe_1GB
The name of the directory depends on the map you have licensed on your TomTom device.
In this folder is a file named MapSettings.cfg. Copy this file to your TomTom device into the map folder (which should be the same as the direcrory mentioned above) and your favorites should be back again.
If you have any information if TomTom changed this behaviour – which in my opinion is a bug – feel free to leave a comment.