Thanks for the reply, I know what you mean!
But they ARE all flac files and look like in the screenshot. Two audio files with the same filename - the smaller one is the cue file and the larger one is the accompanying 'image' file. Used foobar before I found out about the amazing library-options that JRiver has.
Most albums I've ripped with CUETools/CUERipper from the physical cd. There you have the choice to save the album - splitted in seperate tracks, or as an image file, like in the other screenshot.
Mostly classical albums - this way preserves the album exactly like it was pressed. (You even have a 'repair' option for damaged disks!)
You CAN change this afterwards (tracks instead of image) with CUETools - this makes the problem with the playback disappear - but there is no way to 'batch-convert' all the albums, sadly.
Anyway what I found out as an amateur, is that as soon as you interfere (pause, forward, whatever) with the playback, the problem that the user in the older post already noticed does not occur anymore. And 'quickly loading the album again during the silence before the playback starts' also makes JRiver playing the rest smoothly, but that's unsatisfying. For now I'm quite happy with letting foobar run in the background and using the renderer as the output device! Just curious about the 'root' of the problem!
(Edited because of some ugly typos - not a native speaker 😊...)
the screenshots are in the attachment