Could you update the OpenStreeMap tile renders in Garmin Connect Web? The render you are using is ancient. It hasn't been updated even once while I've been a Garmin device user. The area where I live has changed quite a bit in last few years and the OpenStreetMaps has gotten more accurate also. Sadly none of those changes are available in Garmin Connect.
And the second question is that could you just use the original OSM tile renders instead of your custom theme? The original is much more detailed than yours. It would be very handy for trail runners, hikers, MTB, etc.