I would like to note, as my ticket has been closed as a duplicate of this one, that the issue isn't limited to spyglasses but also to normal view, as mobs can appear and dissappear in plain sight as a result of the low entity rendering distance. This isn't an issue in Java as there is an entity rendering distance setting. According to what I can see, it seems that mobs are viewable Max 4 chunks away, and it also seems that they respawn when leaving and entering that distance.
KDBOrion
I would like to note, as my ticket has been closed as a duplicate of this one, that the issue isn't limited to spyglasses but also to normal view, as mobs can appear and dissappear in plain sight as a result of the low entity rendering distance. This isn't an issue in Java as there is an entity rendering distance setting. According to what I can see, it seems that mobs are viewable Max 4 chunks away, and it also seems that they respawn when leaving and entering that distance.