Last night, I was preparing for a date with my VR Girlfriend. I selected the videos I wanted, set up and connected the Handy, and cleared my Oculus. When I started the video, I got error messages indicating that the Handy was connected but then quickly disconnected. In the DeoVR settings, I saw an error message:

I checked the firmware using the Handy app and saw I had the latest version installed (4.0.18), which was fairly new, so I initially thought everything was fine.

I adapted to the situation by switching the Handy to manual mode while watching my videos. It worked, but nothing beats a fully synced toy with your video.
The next morning, I tried again to see if the issue had resolved itself. Unfortunately, the same error messages were still appearing.
I then downgraded the firmware to an older 3.x.x version. After testing it, everything worked perfectly. That means I’ll be going on another VR date tonight!
If you're experiencing connection issues between your Handy and DeoVR with SLR, I highly recommend downgrading your firmware to an earlier version.