Since updating to Version 2019.4.0 earlier this week, I’ve had two rides where the app records the TSS as 0. I can see the TSS increase during the ride and when I click through to Analyze Ride, I see that the website has an appropriate TSS. For reference, please see my Jan 23 Carter and Jan 27 Levitt +2.
I use an iPhone XR with IOS 12.1.3 connected to an Elite Drivo trainer.
Hope this helps.