I installed 6.2, but the situation don't change.

I noticed this:

when arrive first message I don't receive led/sound notifications:

Jun 25 10:17:36 Jolla alien.sh[862]: 06-25 10:17:36.162 2775 8346 E MediaPlayer: Uri is content://settings/system/notification_sound
Jun 25 10:17:36 Jolla alien.sh[862]: 06-25 10:17:36.165 955 1058 E MediaPlayerService: Couldn't open fd for content://settings/system/notification_sound
Jun 25 10:17:36 Jolla alien.sh[862]: 06-25 10:17:36.167 2775 8346 E MediaPlayer: Unable to to create media player
Jun 25 10:17:36 Jolla ons[7112]: [D] NotificationsWatcher::handleNotify:455 - "AndroidNotification" "1 nuovo messaggio" "pippopippo" "/data/notificationIcon/com.whatsapp2130838948.png" QMap(("x-nemo-preview-body", QVariant(QString, "1 nuovo messaggio") ) ( "x-nemo-preview-icon" , QVariant(QString, "/data/notificationIcon/com.whatsapp2130838948.png") ) ( "x-nemo-preview-summary" , QVariant(QString, "pippopippo") ) )


if I don't read it and another message arrives I receive notifications and theese are logs:

Jun 25 10:17:57 Jolla alien.sh[862]: 06-25 10:17:57.992 2775 8355 E MediaPlayer: Uri is content://settings/system/notification_sound
Jun 25 10:17:57 Jolla alien.sh[862]: 06-25 10:17:57.996 955 955 E MediaPlayerService: Couldn't open fd for content://settings/system/notification_sound
Jun 25 10:17:58 Jolla alien.sh[862]: 06-25 10:17:57.997 2775 8355 E MediaPlayer: Unable to to create media player
Jun 25 10:17:58 Jolla ons[7112]: [D] NotificationsWatcher::handleNotify:455 - "AndroidNotification" "2 nuovi messaggi" "pippopippo" "/data/notificationIcon/com.whatsapp2130838948.png" QMap(("x-nemo-preview-body", QVariant(QString, "2 nuovi messaggi") ) ( "x-nemo-preview-icon" , QVariant(QString, "/data/notificationIcon/com.whatsapp2130838948.png") ) ( "x-nemo-preview-summary" , QVariant(QString, "pippopippo") ) )
Jun 25 10:17:58 Jolla ons[7112]: [D] NotificationsWatcher::handleNotification:315 - Faking sound with "chat"
Jun 25 10:17:58 Jolla ons[7112]: [D] NotificationsWatcher::handleNotification:326 - Replacing notification 920
Jun 25 10:17:58 Jolla ons[7112]: [D] NotificationsWatcher::handleNotify:455 - "android-notifications" "" "" "" QMap(("x-nemo-feedback", QVariant(QString, "chat") ) )
Jun 25 10:17:58 Jolla ons[7112]: [D] NotificationsWatcher::handleNotify:455 - "pippopippo" "1 nuovo messaggio" "pippopippo" "/data/notificationIcon/com.whatsapp2130838948.png" QMap(("x-nemo-feedback", QVariant(QString, "chat") ) ( "x-nemo-icon" , QVariant(QString, "/data/notificationIcon/com.whatsapp2130838948.png") ) ( "x-nemo-preview-body" , QVariant(QString, "1 nuovo messaggio") ) ( "x-nemo-preview-icon" , QVariant(QString, "/data/notificationIcon/com.whatsapp2130838948.png") ) ( "x-nemo-preview-summary" , QVariant(QString, "pippopippo") ) ( "x-nemo-priority" , QVariant(QString, "100") ) )

So It seems the problem occurs only at the first notification...
Hope this helps :-)