Amazing work, it's practically the complete game! Picked up on a couple minor new bugs I thought you should know. I've sorted the bugs into the 3 main categories I observed: minimally impactful visual bugs, level transition bugs that impact the fluidity but not the progression of the game, and portal surface bugs, one of which prevented completion of chamber 17. All of these were observed playing version 1.86 on my PCH-2006 Vita using a purchased Steam copy of the game.
Visuals: I just updated from 1.72 to 1.86 and noticed on chamber 11 that the floating square platform has disappeared. I can still track it's position by the glowing orb on the blue light track below, and I can still stand on the invisible platform, but it was definitely visible for me on 1.72. In chamber 16's secret room, the farther half of the floor uses a repeating door texture grid that matches the door with the keycode in the far corner of the same room. Also one of the loading screen tips about restarting if you're soft locked on a level had it spelled "resarting" I believe.
Level Transitions: After completing chamber 14, the game booted me back to the menu where I had to manually select the following chamber. After completing chamber 15, I'm loaded back into the same chamber (no, not 15.2). Completing 15.2 also boots me back to the menu. Restarting chamber 16 sends me to 15.2. Completing chamber 16 had me exiting the elevator out of bounds and physically above the chamber 16 map, I could walk forward and fall back into the map but the open elevator won't close and end the level again. Restarting chamber 17 sends me back to 15.2.
Portal Surfaces: Not sure if this was the case in prior releases of the port, but discovered most clear and frosted windows work as portal surfaces. The final mesh/fence at the end of chamber 16 functioned as a portal surface about half the time. I believe the incidents in chamber 16 may be correlated to glancing angles and close distances, which nearly prevented being able to shoot portals through the fence. In the beginning of chamber 17, the entire white wall plane that the 2nd orb-shooter is aimed at cannot open a portal, soft locking the completion of chamber 17. In the first section of chamber 18, the 6x8 square checkered floor below the exit door will not open a portal. In the 3rd section of chamber 18 (with the series of vertical flings), none of the white walls and ceiling that surround the starting area can open a portal. After reaching the top of this area, there were a number of times I "phase shifted" through the floor and out of bounds while walking to the elevator.
In any case, this is still absolutely amazing progress, and probably the best PC-Vita port of a 3D game from the last 20 years. Totally appreciate what you've accomplished and what you're contributing to this game system's legacy.