Player avatar randomly jumps from mine to ground level

About a week and a half ago, upgraded my phone from old iPhone SE 1st gen to new iPhone SE 2020. Minecraft application and Worlds installed on new iPhone SE 2020 from 1st gen SE via an iCloud Minecraft application and data image. At outset the migration seemed okay.

In the last couple of days, while mining around Y-axis 11, I saw multiple error messages that flashed by too quickly to capture. Something vaguely like object reference not fixed or recorded. Same error message appeared perhaps 6-10 times in quick succession while mining. The font on message wasn't pixelated game font used in MC, rather white, small sized, smooth, and scrolled down the left hand side of play area, if that helps. Then within a short period of time after the error messages (a few seconds to maybe 1-2 minutes), player avatar instantaneously "jumped" from mine level ~Y11 to ground level ~Y69. Since first "jump", I've rebooted the application and phone. Since reboot, this instantaneous "jump" happened a second time.

If it means anything, I mine using lots of torches. Basically putting torches in every block then mining the stone above the torches to clear all the gravel in an area. Forms a large cavern, creates lots of dropped gravel, and creates lots of block changes in a fairly short amount of time.

I'll try to get a log file next time this happens.

Reproducibility: not able to discern a pattern yet. Once I do, I'll come back with details