Thanks for reaching out. Have you tried checking the sub count on Creator Studio? Also, mind sharing screenshots and more info for us to look into it? Keep us posted.
Same thing happened to me i gained 74 subs but the YouTube app says 73
You can add location information to your Tweets, such as your city or precise location, from the web and via third-party applications. You always have the option to delete your Tweet location history. Learn more
Same thing happened to me i gained 74 subs but the YouTube app says 73