Music app: Adding album artwork changed bitrate

[Bill Av]

I was changing the artwork by selecting all the tracks of an album, getting info, then pasting the artwork. I noticed that the file type was changing from Apple Lossless to 256 AAC after I did this. Has anyone else seen this? I went through my library and saw that over 80 albums had similar issues. I rip my CDs as Apple Lossless for home playback, then I create a 128 AAC file for my iOS devices. With these 80 albums, I’m seeing that songs are missing, or I have two AAC files or two Apple Lossless files. I don’t subscribe to Apple Music.