Synology NAS Backup Stalls at 99% During Large File Transfers over Wi-Fi

I recently set up a Synology DS220+ NAS to back up my home PC wirelessly. The backup process runs smoothly until it hits around 99% completion, then it just stalls indefinitely. I've tried connecting both the NAS and my PC to a 5 GHz Wi-Fi network to improve speed and stability, but the issue persists. Restarting the NAS or the router temporarily fixes it, but the problem returns on the next backup attempt. Wired connections aren’t an option right now because my PC is in a room far from the router, and running Ethernet cables isn’t feasible. I’m hoping to get reliable, full backups over Wi-Fi without this annoying stall at the end. Has anyone encountered this with Synology devices? Are there specific settings or firmware updates that might resolve this? Also, could it be related to large file sizes or the backup software itself? Any suggestions on troubleshooting this or alternative wireless backup approaches would be appreciated.