I have the same problem with PDVD 19 ULTRA.
It switches automatically to 2D when I play 3D BDs. I have to manually switch to 3D each and every time I play a 3D BD.
Settings shows: Play 3D media in 3D.
It absolutely refuses to play 3D ISOs or MKV.MVCs, MKV-SBS.
I have no problem playing all these formats with PDVD 17 ULTRA.
PDVD 19 crashes constantly when I try to play 3D BDs or Video Files, had to reintall quite a few times already.
After reinstall I can play 3D BDs and ISOs (ISOs only with a virtual Drive).
I will open a ticket eventually. By the way PDVD 19 Ultra advertises ISO playback but there absolutely no support for them.
I get PDVD does not support playback of this type of file, or something of the sort.
I feel pretty dumb for upgrading to 19 when 17 was working flawlesly...
I have a pretty good HTPC: Intel 6700K, 32 GBs DDR4 RAM, MSI 170A Gaming 7 with SGX, Radeon VII (had a Founder's Edition RTX 2080ti which I sold because it stopped supporting 3D after 418.95).
Does anyone have any real solutions for this?