I can try Resilio also, but i think, i will stay with SynchronizeUltimate. Mostly, since I use this App for all my other backup jobs from phone to the Raspberry Pi since some time (WhatsApp backup, photos, app settings and much more). Since it supports SSH, its nearby perfect for me. I have used it last night the first time for music sync. I have set it up with its own scheduler and some conditions (own WiFi network, charging, sync deletes) and i must say, it worked great. But i will try Resilio to. Thx for the tip.
BTW: I have tried FolderSync to. But FolderSync has so much problems. WebDAV does not work, SSH seems also to be broken. It seems to be more intuitive, but when it wont sync correctly, its not the best solution.