Relationship loss when updating object

I have an Android application where there is a week table and a visit table. The visits table has a 1:n relationship with the week table. In this way, the visit has a reference to the week through an object. However, when updating the week, the visit table loses the week reference. I do not change the primary key, I only update the other fields. What could be happening?

JsonObject semanaJson = semanasArray.get(auxI).getAsJsonObject();

                                Semana semana = (Semana) semanaRepo.getById(semanaJson.get("id").getAsInt());

                                if (semana == null) {
                                    semana = semanaRepo.getObject(semanaJson);
                                }

                                semana.mergeWithJSON(semanaJson);

public void mergeWithJSON(JsonObject jsonObject) {
		@SuppressLint("SimpleDateFormat")
		SimpleDateFormat formatter = new SimpleDateFormat(DateFormats.DATA);

		setNome(jsonObject.get("nome").getAsString());
		try {
			setDiaInicial(formatter.parse(jsonObject.get("data_inicio").getAsString()));
		} catch (ParseException e) {
			Sentry.captureException(e);
			throw new RuntimeException(e);
		}
		try {
			setDiaFinal(formatter.parse(jsonObject.get("data_fim").getAsString()));
		} catch (ParseException e) {
			Sentry.captureException(e);
			throw new RuntimeException(e);
		}

		Date dataInicio = getDiaInicial();
		Date dataFinal = getDiaFinal();
		Calendar cal = Calendar.getInstance();

		cal.setTime(dataInicio);
		cal.set(Calendar.HOUR_OF_DAY, 00);
		cal.set(Calendar.MINUTE, 00);
		cal.set(Calendar.SECOND, 00);
		setDiaInicial(cal.getTime());

		cal.setTime(dataFinal);
		cal.set(Calendar.HOUR_OF_DAY, 23);
		cal.set(Calendar.MINUTE, 59);
		cal.set(Calendar.SECOND, 59);
		setDiaFinal(cal.getTime());
	}