I'm using openVPN, server intalled directly on the NAS machine. But I once had Wireguard on a raspberryPI serving as VPN as well. In both cases I remember that I could access my NAS shares from My Files app in Samsung, but not from Launchbox. Other apps were working as well (ex. the synology apps for music, videos, photos, etc.). So (without being 100% sure) I would bet it may be something in Launchbox android app that is preventing reading the NAS shares while on VPN.