Whats the output of smbclient -U USERNAME -Lm ip.of.routersmbclient -U USERNAME -L ip.of.router
Have you considered mounting your shares with:
You should get better throughput and can revert to using smbv3, which is more secure; which should resolve playback issues. Will also resolve the backup issue you are having, you will need to change the backup path to the new share (same with sources for your videos).