Unfortunately I don't have a 3D TV so I can't really help much, I don't even think it's a feature sold on new TV's now, the only thing I can think it may be is that something broke in the newer libamcodec that we are using or the feature is broke in Kodi but without a way to test I can't help sorry.
kszaq mentioned the following:
This PR introduced 3D autoswitch in Kodi Leia: Fix 3d mode switching for Wetek HUB on Libreelec by Memphiz · Pull Request #12316 · xbmc/xbmc · GitHub
If it doesn't work, something is broken upstream.
Do you know, if this fix is included in your Leia-version?
If not, how can this be achieved?
I think in an official Leia version all fixes from a previous version should be contained...