Dropping the bow arm to look for the arrow causes low hits.That might be part of the reason,drop arm one time but not the next.
Most likely the main issue is not a proper aim/release sequence.You need to be letting the pin float on the spot,do not try to force it to stop on the spot.That will cause the arrows to miss the spot.(think about it this way,if you are forcing the pin ON the spot,where will the pin go when it moves.Off the spot.But,if the pin is floating,the pin continually comes back to center.)Secondly,the release needs to be fired with a surprise release.This way you are not pulling the pin off the spot when the release goes off.
Light trigger pull also causes alot of issues like this.They do not allow you to settle the pin on the spot while letting it float and applying slow pressure to get a surprise release.