Groove's managed package inserts new tasks and events into Salesforce using an APEX trigger. Using this APEX trigger allows Groove do things like automatically associate tasks and events to open opportunities related to a contact/account.
Process actions dependent on the Who/What ID
Due to a nuance in the order of how Salesforce processes new tasks/events created using an APEX trigger, sometimes the who/what ID on activities are not immediately populated. This means any process actions dependent on the Who or What ID of an activity will not always fire.
To workaround this, you will need to add a slight delay before the action in your process is triggered for newly created activities.
A delay of '0 hours after LastModifiedDate' will be a long enough delay. After this delay is added, any actions dependent on the who/what ID of a task will fire properly.