Terrain become transparent mostly when re-entering game

This problem started happening after the Bedrock update of two weeks ago. When a player starts the game on my Bedrock SMP server, the terrain becomes transparent and one can see into the underworld or through walls. Nearby chunks don't render and chunks 50-200 blocks away render slowly. The rendering glitch also happens at other times.

A possibly related issue involves the transition through Nether portals. Transition takes longer than normal, sounds are choppy and weird, and players sometimes spawn in a featureless void. I one case, my character died by suffocation in solid rock.