Last spring I bought a new Guardian and it was 60lbs. A month later the shop put a new G5 string on it because something was wrong with the other one. I put my bow on the scale the other day and it tops out at 55.8lbs. Is this from the string stretching? If so is it common to lose this much weight?

The cables and timing need to be reset. It's the cables that effect the poundage most.

You may also want to try another scale or two. Sometimes scales can be misleading.

Beyond trying a different scale, did you checked your ATA, brace height, and cam timing after putting on the new string? After a year of shooting you need to check all of that.In reality that should be checked quit often.

If the ATA is long the limbs are not loading properly and the DW will be lower. Your ATA could be on but your brace height off. Again, changing the DW. Even a shop can't simply put a string on and have everything correct from the beginning.

One other point, did they put on the correct length of string. If not, it wouldn't be the 1st time that has happened in a shop.