A week ago I got some updates related to Samba and now authentication is broken. Windows and Android machines can connect to a Samba server just right, however Ubuntu rejects login credentials. This regression is applied on all Linux flavors sharing Ubuntu repository like Mint or Elementary OS. I hope downgrade instructions can be applied for all Linux.
Debian and Ubuntu don't support downgrading, so you might encounter further problems by applying this piece of advice.
According to the related question on AskUbuntu, you can:
Find out what other versions of Samba are available:
sudo apt-cache showpkg samba
Install that particular version (
sudo apt-get install samba=1.2.3+dfsg-0ubuntu1
Ask the OS not to upgrade the package automatically anymore:
sudo apt-mark hold samba
samba won't be upgraded anymore, this might block other updates.
Also, you'll have to follow the updates (by regularly running
apt-cache showpkg samba, for example) to see when a suitable update appears.