i havent looked at the parsing code in sonarr but its standard practice to put the year in brackets after the name when there are multiple shows with the same name, eg vikings, and vikings (2013).
i’ve never seen anyone put the series/ep numbers in brackets before but its up to them if they want to do their own thing.
if you put vikings s06e10 into the manual jackett search do you get any returns?
just that sonarr doesnt search for vikings, it includes the season/ep in there as well so you need to match the search query (which should be i the debug logs) to see what it would find.