Thank you for your inquiry. As you seem to be aware, the leaves of serviceberry trees (Amelanchier) turn red in the fall. Even though it’s difficult to discern clearly from your photo whether the leaves have become prematurely red or if the tree might be diseased [and/or suffering some stress], I suspect that it is the former. Please see: https://www.torontomastergardeners.ca/askagardener/a-few-of-my-serviceberry-trees-leaves-have-turned-red-even-though-its-just-summer/
Given the ample amount of rain that we’ve experienced this spring/summer in southern Ontario, compared to previous years, it’s possible that the tree simply has completed its growth cycle earlier than usual. Serviceberries do prefer well-drained soil–even though they can adapt to clay soils, using an organic mulch around the base of your tree as you describe, will gradually improve the drainage of the soil. As advised in the above link, if the leaves continue to fall or if you notice any of the described disease issues, please contact us again.
https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=j290