I see that you're having an issue with trying to rewind and fast forward a song on your iPhone. I can understand your concern since it was working and then it stopped, and I'd be happy to help.
Let's make sure that you're using the latest software on your iPhone first. Go to Settings > General > About. The latest version is 11.2. If you're not running iOS 11.2, go ahead and update:
Update the iOS on your iPhone, iPad, or iPod touch
If you're already up to date go ahead and try and restart your iPhone and see if the issue remains:
Restart your iPhone, iPad, or iPod touch
If after going through these steps the issue still remains, reply back with the answers to the following questions.
1. Are you an Apple Music member?
2. Does this happen when using the Music app or other music Apps?
Thank you for using Apple Support Communities.
Have a great day!