There seems to be a problem with macOS APFS drives, in part because of the weird games Apple play with maintaining snapshots on these drives.
For example right now I have a 1TB drive I use for Channels.
- Channels claims there is only 1.52G available, and refuses to record
- Finder says there is
- 193.88GB available, 192.27GB purgeable
- 998,170,664,960 bytes used (but as I say, 190G of that is basically purgeable)
My analysis is that there is plenty of space available, but Channels is not querying the file system for the 'correct" version of available space, and needs to be updated to handle this, uh, quirk, of APFS. Either query the "real" amount of available space, or, when the amount of available space looks like it's low, force a purge, then re-query how much space is available.