We have addressed the issues reported in the 「バグ報告スレッド（日本語ver）」 and released an update as “v1.0.2-4.” Thank you very much for your reports 🙇♂️
Fix Details
Fixed an issue where the game could become unplayable when the BGM switched after clearing Stage 5-6.
If you encounter a similar issue in “v1.0.2-4” or later, it would be greatly appreciated if you could let us know here or in the bug report thread, along with your OS and version information.