Spawnrate Minecraft error

Environmental spawning in Bedrock Edition shares broad similarities to natural spawning in Java Edition: mobs spawn in a radius around the player subject to block conditions, lighting conditions, biome conditions, naturally generated structure conditions, and caps.
In my case simulation distance 4: between 24 and 44 blocks spherical radius from the player.
Mobs spawn according to the game algorithm, but then disappear
Conducted a lot of experiments, but despite the number of mobs within 100 blocks of the "mob farm", I came to the conclusion that this is some kind of bug that removes mobs contrary to the algorithm to limit all mobs.
It is interesting to know what I did not take into account when checking all this, I will be glad to discuss this topic.
P. s. Attached a video demonstrating this bug or a game error.