It seems like you're encountering an issue with your formula and the connector you're using. The error message suggests that the "CountIf" operation is not supported by the connector you're using in your roll call app. This might explain why your formula is not returning the expected result.
To work around this issue, you can try using the "Filter" function instead of "CountIf" to achieve the desired result. Here's an example formula that should help you count the number of employees on site who are fire marshals:
COUNT(FILTER('Fire Safety Employee Checklist', Onsite = true, Responsibility = "Fire Marshall"))
This formula uses the "Filter" function to create a filtered view of the 'Fire Safety Employee Checklist' based on the conditions specified. It then uses the "Count" function to count the number of rows in the filtered view, which corresponds to the number of employees on site who are fire marshals.
Give this formula a try and see if it returns the correct count for you.