GigaVanilla

I believe the crash issue was caused by the game being unable to find a spawnable block in the very small number of blocks available to be spawned on because the only locations the game was trying to use where from a single straight line of blocks. Lowering the spawn radius on a semi-anarchy server lead to players getting spawn camped so having the spawn radius high is kind of necessary.

I had immediate respawn on
I died over and over using /kill
the world was a layer of bedrock and a layer of black concrete with structures turned off, freshly generated on a vanilla client on the latest stable release of 26.1.1
amd processor nvidia gpu

At respawn radius 0 the spawn was 0 0
at respawn radius 10 behavior seems normal
at respawn radius 20 the highest z value was positive 1
at 30 the highest z value was -14
at 128 the highest z value was -124
at 512 the only observed z value was -511
For clarity by “highest” i mean most positive, so 10 is higher than -20.
The z values at any respawn radius above 10 skew very negative, and at higher values the game will only chose to spawn at the edge of possible values.

This issue is a pain to deal with as a server owner, it also seems to cause the game to hang on a tick for 60 seconds causing watchdog to crash the server when a player tries to respawn without a bed or other spawnpoint set intermittently, maybe 5% of the time, on the latest update I have not seen this crash.