Logic Pro X takes very long to load

Hi, I have a 2013 21.5 inch iMac and I use it almost exclusively for Logic. Recently I started having a problem where every time I open one of my nearly mixed songs, I get the message "additional content needs to be downloaded" even though it already is. The song consists mainly of studio strings and horns, with two Yamaha grand piano's and a drummer and a few audio tracks. The real problem is that none of the instruments have the right sounds until I download the 2.9 GB worth of sounds which for some reason it is. Every track has either the sound of a drum kit or the default electric vintage piano. I get very frustrated having to wait half an hour to start editing the song, only to find that the smart controls and EQ for some of the tracks have also reverted to default which screws up the sound of the song anyway, and then when I close it and open it a few days later I have to go through the whole process again. This happens with a few of my projects, and the one I'm talking about in particular is only just over 2 minutes long!

If anyone has any idea what could be causing this or how to fix it, it would be incredibly appreciated.