I use FanGraphs for searching baseball players, which I access via Kagi using the !fg hashbang.
It seems like a few months ago they changed the query parameter for search from lastname to q. You can see this when you search via hashbang, which will take you to a URL like: https://www.fangraphs.com/search?lastname=abc
If you use the website's search it will instead take you to a URL like this, which uses q instead of lastname: https://www.fangraphs.com/search?q=abc
The correct fix is simple, to change the query parameter used for the !fg hashbang. Happy to provide more details if needed.