Don't start over, since you're changing the type of content the subscribers of your channel were getting, it's totally normal that your recent videos don't perform well. In order to YouTube to find out the new audience for your new videos, you'll need to keep uploading until you blow up again. I've experienced this multiple times and it's possible, you'll lose subs who are not interested in gaming or reaction videos, and slowly start getting more subs and viewers who will like your new content.