When you are in the menu to select a sample folder, and you select a specific sample in that folder/directory, it actually doesn’t matter which sample you pick - buoys will try to load that whole folder in (I think) alphabetical order. This is probably a bit non-intuitive but it’s a shortcut I took in order to be able to use a particular helper library for navigating the file structure (I will very likely try to improve this experience in future versions). The total sample length that can be loaded into buoys is currently ~349 seconds. So I suspect what is happening is when you try to load a particular tape file, the other tape files that came before it alphabetically in that directory are filling up the available space in the audio buffer. If that doesn’t jibe with what you’re seeing, please let me know.
Sorry for the suboptimal experience. Until I find a more elegant in-app approach, a solution would be to connect to the norns filesystem (https://monome.org/docs/norns/fileshare/) and create a new folder in the audio directory, and just move the tapes you’d like to use with buoys into their own folder. If you don’t want to move the existing files, you could also create aliases/symlinks and just put those into their own folder.