I have a superflat world in which I am building a redstone-heavy project. The redstone is all up near the upper build limit, with some non-redstone areas are being built below.
After working on one area for a couple hours, I found that returning to the upper redstone area consistently causes a hard freeze. I have been able to move within one block of the redstone area without freezing by looking down and flying upward, but looking up or getting next to it causes an immediate freeze.
The problem area has around 30 double chests, lots of redstone (no clocks, very few pistons, mostly tripwire-triggered latch arrays etc.) It also has a board with about 30 item frames and different armor, potions, and weapons. I suspect the item frames may be causing the freeze as the it seems that about 32 blocks is the radius to keep from freezing. Further evidence of this is that averting the eyes seems to help to a point (item frames don't render unless you look toward them, right?).
I could provide a raw copy of the world if needed. If possible, a fix would be nice.
EDIT: I have collected more data. The outer bounds of the crash area are
(-66, 235, 145) from the south
(-66, 235, -12) from the north
This suggests a length of ~157 blocks
This data led me to approach from the midpoint Z=67 line
(-20, 235, 67) from the east
(-108, 235, 67) from the west
This suggests a width of ~88 blocks
There are item frames in two general locations,
~(-62,235,98) is the main board of item frames. This is
~50 blocks from the south bound
~52 blocks from the east bound
~55 blocks from the west bound
~110 blocks from north bound – suggesting a second problem location
It is also notable that approaching from above freezes at (-62, 283, 98), which is 48 blocks away from the main board of item frames.
~(-64,235,31) there are about four to five item frames spread out a little
This happens to be about 43 blocks from the north bound.
Distances were calculated using two-dimensional distance formulas as all the Y values are the same.
I can conclude that whatever is causing the problem is centered around the only two areas with item frames, with a crash distance of about 45 - 55 blocks.