The render distance gets reduced to the lowest value randomly, sometimes it looks like it’s related to the game performance. But if you access to settings, you will see the correct render distance that you have previously, but it doesn’t shows in game, it looks like the lowest render distance. For example, I have the render distance set up to 12 chunks, I start playing and when I’m in a busy zone, the screen flickers for 1 second, and the render distance sets to the lowest, even if in the settings says 12 chunks, It’s imposible to see the 12 chunks render distance, unless I exit the world/realm and load it again. This happened to me in the 1.21.72 version, it started in that version, but now it’s much more frequent.
This issue is being tracked at MCPE-216671.