Dynamic's SynchronousUpdating->False broken in Graphics

Question

Bug reproduced in V10.4.1 and persisting through V11.2

A support case with the identification [CASE:3699190] was created.

[...] It does appear that SynchronousUpdating -> False is not interacting with CacheGraphics properly. I have forwarded an incident report to our developers with the information you provided. [...]

---

When Dynamic content is bigger, the updating is broken:

data = RandomReal[{-1, 1}, {10^4, 2}];
show = False;

Checkbox[Dynamic@show]

Dynamic[
   If[  TrueQ@show, Length[data], "not shown"], 
   SynchronousUpdating -> False
]

Graphics[{
  Dynamic[
    If[TrueQ@show, Line[data], {}], 
    SynchronousUpdating -> False
  ]}, 
  PlotRange -> 1, Frame -> True]

As we can see Length is updated correctly while the plot remains populated and only flashes during next switch.

It won't happen if data is smaller, e.g 10^2.

Answer 1

It seems to be another "feature" related to CacheGraphics, this will work correctly:

Graphics[{
   Dynamic[
     If[TrueQ @ show, Line[data], {}], 
     SynchronousUpdating -> False
   ]}, 
   PlotRange -> 1, 
   Frame -> True, 
   BaseStyle -> CacheGraphics -> False
]

Another because we already know that: Transparent bitmaps or graphics in gui objects initially appear wrong