While Tesla used to support WMA, I thought they dropped it several years ago. The loading error used to be more common in the 2018-2020 timeframe, mostly with MP3, but it's rare to hear of it today. If you're using a HUB, try it without the hub. Not sure what else to suggest. Have you tried MP3 files? Not that you'd want to switch from FLAC, but as a test. I assume all FLAC files are the same. I use Media Monkey to code my FLAC files mostly at 44.1 kHz sample rate, with VBR off. Higher rates were supported in the past too. I know Tesla only supports two channels, but if you're using more channels, I thought it ignores the extra channels. I've not tested > 2 channels in FLAC.