Stereo to Mono Conversion Prevents Playback and Stereo Tracks Warped Even in Previous Save

I tried to convert stereo tracks to mono using the media pool>covert>replace and it completely prevents Cubase from playing back. The “play” button is green meaning engaged yet the cursor doesn’t move along the tracks. It will jump rarely and let out some sound, but it is completely unable to playback.

I saved the previous state of this and went back to try again without plugins attached. I went to convert stereo to mono and the result was time warped , crunched and zany. Again going back to my previous save, to find that despite it being pre-conversion, all of the audio tracks are time warped in the same way. The audio in the track is crunched, but the track itself continues on for the length it was.

What’s going on, why am I having so many issues with turning stereo tracks into mono?
I am developing my methods still, and I was going to try dual-panning, and mixing down as well but, now the tracks are ruined as far as I can tell. How did it affect the previous save?

BTW, I never changed recording format. I can see in the media pool that those were never altered!