Edited, thanks for mentioning that.
This issue is still present in 1.19.21, I am able to reproduce and it has caused me to lose 2 tadpoles.
I looked into this issue as it was happening on my realm, it is likely a resource pack issue. One of the addons I had been using (Modded Cursed Unobtainable) was causing the issue, as it uses a file that does not exist as a bottom texture for purpur. If you have this addon and are experiencing this issue, that is why.
Can confirm. Me and my friend were playing on a realm, and we went to the end, and immediately when we spawned I was halfway in the obsidian platform and I watched my friend's name tag as he fell into the void. We were at the correct coordinates. This has never happened before, and this realm has existed for two years. I believe the newest update causes it (1.19.30)