I can't complete either achievement in 1.19.51. Super Sonic is being tracked at MCPE-55142; but I couldn't find any ticket open for So I got that going for me.
This has happened to me 3 times now. The issue seems to be that if you get stuck in the "Generating World" screen when entering a portal, after closing the game and logging back in, you are sent to the dimension you were trying to get into; but with the coordinates you were in. For example, if you are traveling from the Overworld to the Nether at the coordinates 800,-20,1600, your game freezes while generating the world and restart the game, you'll be in the Nether, but instead of being at coordinates 100,5,200, you'll be at 800,-20,1600, and therefore you'll fall into the void.
I noticed this because the first time this happened to me, I was traveling from the Nether to the Overworld, and instead of being at 0,64,800, where the portal is, I was at 0,11,100. I did happen to spawn inside rock and I suffocated while I was there, but I survived because of a totem I had and mining as soon as I could.
The second instance was when I was traveling to the Nether and exactly the opposite happened. I was located at 0,64,800 in the Nether instead of at 0,11,100, forcing me to travel to the portal.
And the third time, I traveled from an underground portal towards the Nether, but I spawned in the void with no way out but hunger documented here.
https://www.reddit.com/r/Minecraft/comments/ystjkj/
What I believe happened to Adam Cox and their son was the Overworld portal was below 0, and they simply fell into the void.
Edit as of 1st-Dec-2022: As a note, I was playing locally on my Switch, but since I passed the save to a realm and I've been playing on PC, the load times are reduced significantly, and I haven't been stuck in the "Generating World" screen for more than 10 seconds since then. Might be a realm thing though, since I haven't attempted to do it locally.
This is still an ongoing issue in 1,19.51.
https://gfycat.com/clearunacceptablebovine