Long audio previews do not repeat
It's known issue, already reported in #23575 (in Japanese).
DTXMania uses two ways to playback audio. One is on-memory playback, and another is streaming playback.
Which playback way is used? It depends on the audio payload size. If the size is smaller than 3000000 bytes, then on-memory playback is used. If bigger, streaming is used.
And, as you know, streaming playback has a bug that it doesn't repeat.
It seems it's the bug in SoundDecoder.dll, but no one has a sourcecode for that dll. So the fixing is pending at now....
When listening to a song's audio preview in-game, some previews do not repeat after the first time through.
Same compression, differences: ~17sec, ~261KB, DOES repeat / ~21sec, ~328KB, DOES NOT repeat