A bug in gpxpy, tkrajina/gpxpy#277, can cause invalid xml to be written in the case that gpx extension fields such as departure callout contain '&' or '<'.
We could implement a workaround in the short term, but it should really be fixed in gpxpy.
Hopefully there will be a new gpxpy release soon, if not we can integrate the fixed branch with a git submodule or something. I'm not sure what the easiest solution is.
A bug in gpxpy, tkrajina/gpxpy#277, can cause invalid xml to be written in the case that gpx extension fields such as departure callout contain '&' or '<'.
We could implement a workaround in the short term, but it should really be fixed in gpxpy.