Do you have writing tags as genre enabled in options? Or did you previously use some plugin like last.fm? The last.fm plugins stopped working a while ago after some changes by last.fm. I don’t currently about the current state and which plugins have been adapted already.
Where do you see the slashes? I don’t think Picard writes slashes here, unless that changed recently.
If you are looking for something with MusicBrainz support, try Jaikoz
Just make sure our let us know what problems you face, otherwise nobody might know. For specific issues or feature wishes best is to open a ticket on https://tickets.musicbrainz.org