Rendering Glitches/Artifacts During & After Transitions

I just ... I know this exists in a lot of different posts already, but I need to vent somewhere because I am just at my wit's end.

Using OSX (latest), and the latest version of Premiere, I have switched my graphics rendered multiple times, and am I am now having issues simply stitching two clips together with transitions. 

Both clips are truncated versions of longer ones (manually cut in the timeline and shortened). The first clip has it's speed reduced to 50%, and the second is normal. When I use a cross dissolve between the two (<1 sec), I see, in the cross dissolve, additional 'tail' from the first clip that I cut, which I understand (the nature of a cross dissolve), however, it doesnt seem like the speed reduction is applied to that part, so there's this weird acceleration in the clip during the transition

Even more frustratingly, once I deleted the transition, the clip had been inexplicably altered, to where the very last few frames of the truncated clip now suddenly "reset" to the beginning few frames. So there's this awkward jump at the end of the clip as if the playhead rewound back to the beginning.

I'm pressed against a deadline, and now im battling with software over something that used to be objectively simple, and im about to flip out.