Words are missing after migrating from Wokabulary 5 to 6
Please note that Wokabulary 5 and Wokabulary 6 are completely separate apps and don't sync with each other.
So, if you had tried Wokabulary 6 at some point before, all your data will have been imported back then and does not reflect any changes you might have made afterward in Wokabulary 5.
In that case, however, you can manually export the current state of your vocabularies from Wokabulary 5 and import it again in Wokabulary 6.
Tip
If you have just used Wokabulary 6 for the first time, please note that the initial sync of your words to all your devices can take a couple of minutes. For example, if you have first started Wokabulary 6 on your Mac, all your data is imported there. But it will take a bit until it is completely synced to your iPhone or iPad.