World used was created in 21w41a, updated through 21w42a and finally used in 21w43a.

Issue encountered when rendering new chunks, so may simply be extension of MC-239878, but crash report attached.

Notable performance issues prior to crash a few minutes after launching having rendered new chunks, the previous time these issues were encountered, game completed execution successfully.

Crash occurred on save and exit after performance issues were noticed. Prior to this, killed drowned wielding trident, swam to boat, traveled to previously loaded chunks possibly out of render distance of new chunks, killed second drowned wielding trident, broke block underwater. Chest would not open, experienced low framerates, could not enter boat.