Satellites are not in perfect position. They do course corrections on a regular basis. Observing from the ground the satellites wobble up and down in their orbit over a 24 hour period, and move east west usually on a weekly pattern. If your alignment is off the satellite can cycle off and on during the day as it just moves out of position enough for you to lose signal.
Alignment is the orientation if the dish. Line of site is related to objects obstructing the signal from reaching the dish. The most common obstruction is foliage such as that from trees. As the limbs blow around in the wind the signal can be obstructed.