Ok, I know you are thinking is not your problem but depends on custom rom so maybe phone brand developers will solve the problem but I'm 99% sure that there is a conflict in your app.
Atm, I can choose many different combinations of notify in your app and some are not compatible but for us is too hard to check all and remember what works and what not.
1. In setting we can choose the graphic, big or default.
2. For each medicine we can choose recurring and/or importance (Here I have a conflict, if I choose botch the notify sound not works).
3. Other 3 choice under Android Notify Menu for sound about Relevant, content and therapy ( I think to have here an other conflict, if I change sound for therapy it's change for all the default app or even worst disable all the sound for al the apps).
4. Override on ND that there isn't on my phone.
So 2 graphic, 3 sound, 2 type checkable, 233=18 combinations. I have to add how we can choose the sounds, 2 way (themes and ringtone) that after a lot of try for me became the same link but inside theme I can choose 4 options, theme sounds (pre-installed), and the old ringtone menu (Local) with other 3 options, recorder, file manager and music and seems that they have a different behavior. Even worse the last part change if the custom optimization of the rom is on or off.
Know seems that some of this choice change not only your app but also default choice of the phone and the unique way to turn back is to change the default sound in Message app.
After 2 days of testing I seems I can choose only relevant or default not both or I have no sound but I don't understood how your app take the sound from the phone and for sure not work's (maybe you not ask the phone for a choice but only let the phone start a default choice).
In all this mess there are a lot of glitch clicking notification but is not my work.
I don't understood also the difference from relevant or important, will be our decisione 1. the sound 2. how many time the app have to bother me and the time between the notification (recursive and important can have a meaning for a developer but not for a user)
I think you have to test better your app and make only a way of configuration, first of all remove global configuration than: new medicine and in that page, sound ( maybe direct choice from file or your sound), how many time to repeat and how how much time between one repetition and another so is clear for young people like me or old people like my father that prefer a paper diary instead of all this chaos.
Good work