Alias by $tag not working after upgrade to 6.6.0


I was using Grafana 5.4.3 and alias by $tag_ was working fine, but not anymore since I upgraded to 6.6.0.

It is now showing a “!” on top left of the chart with “n is not a function”,
when I edit this panel, it is working if I remove the alias by $tag_ but if I put it back it shows an error :

I also tried the [[tag_name]] syntaxe but still the same, did anybody encounter the same issue?