Hi @svcDataflows,
This Canvas API endpoint returns grade values as floats, full stop. To my knowledge, it's always worked this way and therefore is neither an "intended change" nor a "defect"; it's just the expected behavior from the Canvas API.
I can't speak to how your Power Apps custom connector might be trying to use the Canvas data, but it seems confusing to me that it would expect numerical values to come in as strings. To my knowledge, the Power Platform currently only supports the float type for numerical data. If your custom connector is expecting strings, it's most likely internally converting them to floats in order to perform further calculations on them.
f this were my project, my first instinct would be to tear into your custom connector to see if it can me modified to accept the floats from the Canvas API as input.
Steven