I'm not familiar with Garmin plotters. But I have seen issues like this in PC based software plotters. When I observe the issues you are facing I turn off chart quilting and all is good. Any single chart displayed for the area will be displayed accurately, the boat's position plotted accurately and routes and waypoints displayed accurately. It's a bit of a PIA to have to manually select charts in the troubled display area, but it works.
Here's an example from my back yard. OpenCPN displaying NOAA raster charts. With quilting enabled OpenCPN choosed a poor overlay near the entrance to Oak Harbor and some zoom scales.
Garmin should address this, but for now, if you can turn off quilting you may have a work around.