This is nearly identical to my experience on a 1st-gen rPi. After the March 2018 upgrade, SMB became unstable (would sometimes hang) so I switched to NFS and things were fine.
Then, a week or so later, playing video also started to hang the player. Loading the file I was streaming over NFS onto a USB stick, plugging that into the rPi, and playing that way also started to freeze/hang (eliminating the network, NFS vs. SMB, the fileserver, etc).
At that point I realized that the PSU (tiny wall wart) that I’ve been using for a few years for it had likely aged out, or the power requirements for the system post-upgrade were slightly higher. Swapped in a new PSU with better specs and everything is fine again – the same videos that would hang even playing locally were now flawlessly streamed over NFS. I haven’t tried going back to SMB yet.