The owner of GPSies sold their web site to AllTrails, which subsequently closed the APIs that MyTrails was using to upload and download tracks. I will remove the integration in a later version of MyTrails, but for now MyTrails will just display an error when you try to use GPSies.
I’m assured that MyTrails.com.au is still operational and has no plans to shut down or sell out. Feel free to use it for all your track sharing needs (uploading and downloading).
(note that despite the fact that My Trails the web site and MyTrails the app share a name and a good working relationship, they are operated independently – if you need support for the app, use mytrails.app; if you need support for the site, use mytrails.com.au)