The bug

When moving far away from spawn area, chunks near the edge of player view distance don't get sent to the client. This makes the effective render distance artificially smaller. And this applies even if the chunks near the edge of view distance are all already generated (unlike in 1.12.x, where it would only be an issue in newly generated areas).

By looking at MultiplayerChunkCache value, it seems like the client has 1 extra chunk radius of cache, so render distance 10 has space for 529 instead of 441 chunks. After a bit of moving around, the amount of loaded chunks drops to 340 and even below 300 after world reload. The visible effects of this can be seen on attached screenshots. For comparison, also added screenshot after changing render distance to higher value, and then back to 10.