Why are the plastic bag designs different? Bag 4 looks normal, but are the rest legitimate LEGO designs?
First of all, congratulations on securing a 75054 AT-AT. This is a very desirable set, and costs a pretty penny to purchase now that LEGO has stopped producing the set.

There is nothing wrong with your bags. The bags with the white band are of a newer design than the bag labeled "4". The white-band style was introduced in 2015, whereas the older style was used as of 2011. LEGO is slowly phasing out the older style in favor of the white-band style, working through remaining supplies of the latter until they run out.