I really don't know what's the problem with the converter. There was no change within the last couple of weeks.
We use https://github.com/glennreyes/runtastic-gpx
this tool in the background.
Without having the backup (uploads are deleted after 24 hours) we don't know what's wrong.
Please open a ticket there -> https://github.com/glennreyes/runtastic-gpx/issues
We don't have enough time to check it at RUNALYZE.
I don't really recommend to continue using Runtastic. And if you want to have a "Runtastic Sync" have a look at https://www.rungap.com/
If you are using an iPhone use the great iSmoothRun App or HealthFit to record and sync activities to RUNALYZE