The title mentions a light bow, while the body text refers to a long sword, but based on the context, I will answer assuming it is about the light bowgun.
Since there is no image, this is just a guess, but is it possible that the gyro button at the top right of the screen is set to SEMI? If so, tap it and switch it to FULL.
Thank you for your report and we apologize for any inconvenience caused by this.
We’d like to start investigating this case, so could you please check if this issue happens when hunting specific monsters or does this happen for all monsters?
Moreover, please provide us a video/screen recording showing the issue.
Rest assured that we will look into this once we receive a reply from you. Thank you for your patience and cooperation on this.