I just noticed this today with a few WMA lossless files. I tried playing them on the server PC itself with the 127.0.0.1 address, and I'm on Version 1.1.4.2757, Windows 10. I have a few albums in this format and playback skips about half of the tracks, going directly to the next song until Plex finds one it can actually play fully. I've tried playing the songs on VLC media player without any issue, and had no problem playing them a few weeks ago.
All of the past threads regarding playback skipping seem to be with FLAC but I'm not having trouble with that file format at all.