Geocoding addresses (required if you do not have longitude and latitude for your tasks) can be done in Tasks ⇒ Import ⇒ Geocoding ⇒ Geocode Addresses.
For more information on how to import your tasks, please refer to this article.
In case there is an issue with geocoding, there is a possibility of changing the location provider.
You can do this in Configuration ⇒ Address Lookup / Geocoding.
It's important to keep in mind that coordinates are used first, then address. That being said, here are some ways of avoiding location geocoding issues, especially when importing via API:
Send updated coordinates within the task data
Use geocoding - send location info without coordinates and the system will geocode it for you. Please keep in mind that the system will use the first result returned by the geocoding provider based on provided inputs, and quality of geocoding will largely depend on quality of provided address information. you may notice a slight difference in the results. Since the results are based on the 3rd party provider's data, at times a few addresses may fail to be geocoded (even by both providers) based on the input or the location hasn't been registered in the 3rd party provider's database.