Does the issue occur in the editor or during gameplay?
If it's a gameplay issue, please specify which movement system and camera type you're using (free movement vs. grid movement, third-person vs. first-person) or N/A if not applicable:
Briefly describe the issue you're experiencing:
Containers that are set to a custom made widget with more slots than the default 10 are not recognised by the game until the container is opened first.
This affects scripts with commands like add_to_container() which try to fill all the custom slots as it only gives enough items to populate the first 10 slots.
[Gif of the issue demonstrated using print()]

Are there any errors in the in-game debug console or external console window?
Provide the steps necessary to reproduce the issue:
- create a custom widget with 11+ item slots
- Place a object on map and make it a container set to the above widget
- playtest and print the inventory size of the container
- interact with it, and print again
Provide a download link to the bare bones project (strongly recommended if it's an in-game issue, since this helps significantly when attempting to reproduce it; the report will also be given more priority in this case):
Will provide if necessary