FFMPEG HEVC playback all glitchy in PP2019. AME2019 transcodes just fine.

We utilize scripting to create *shudder* many, many different encodes via commandline FFMPEG.

Everything on earth is happy with the encodes, including Adobe Media Encoder.  But importing them into Premiere yields video that quickly falls out of sync (if it imports at all) and the video jumps backward in flash-frames.  Trippy.

I called Adobe and they verified the weird playback and simply said "then don't use FFMPEG".  Sigh.  I just...ugh.

Is there something in particular that is throwing Premiere off?  I've tried CRF and CBR.  Neither work.  Is it the number of b-frames or something along those lines?  What exactly is Premiere tripping over here?  These are bog-standard -preset "medium" FFMPEG encodes.

Seeing as AME can transcode them to something else--and those files import and play back properly--why can't Premiere?  Isn't AME essentially the render module of Premiere?

Hoping to glean an answer here.  It doesn't seem like a lot of FFMPEG guys bring their stuff back into Premiere (yes I realize HEVC it is not an editing codec, but we've had our bacon saved a few times by having a deliverable available to grab shots from in a jamb).