Glad the Run time and TextToSpeech code suggested are working.
You are coding on an ios device. App Inventor for ios is still VERY buggy.
Perhaps this discussion applies TinyDB-problem with iOS with respect for ios Projects and TinyDB use.
Do be aware, your markers stored in the TinyDB doesn't have any associated code to load the 'saved location information on Screen1.Initialize to your markers List , saving markers alone is not going to accomplish this. Saving and reloading Runtime markers has to be done using additional code to re-initialize run time markers using the CreateMarker block. Perhaps use the methodology shown in the NationalPark Tutorial. I think you should be save the Marker data stored as a csv and use that csv to repopulate markers or something like that. I can only guess.