Debugger expression evaluator sometimes replaced by <not accessible> [0]

Sometimes, when I expand a nested element under "this" in the "locals" expression evaluator, the value of "this" becomes <not accessible> and its subtree gets replaced by [0] -> (empty cell).

Double-clicking either cell, and pressing Enter or clicking away, reloads the entire tree containing "this". If you continue expanding nested elements, this bug will recur every second time you expand a new element. Expanding elements will take turns being fast, and being slow and turning "this" empty.

Expanding elements other than "this" will not cause any variable to disappear.

Reproduction instructions:

• git clone -b refactor https://github.com/vgmtrans/vgmtrans
• cd vgmtrans
• git submodule update --init --recursive
• Open CMakeLists.txt in Qt Creator, and configure using MSVC 2017 x64.
• Set a breakpoint on src\main\formats\AkaoSeq.cpp:81 "if (!instrset->LoadVGMFile()) {".
• Debug the program, with CMake set to debug configuration.
• Drag the file 120 Dream's Creation.psf into the program. Note that if you let the program continue executing, it will crash; this is a bug in the program.
• When the breakpoint fires, start expanding the "this" tree in the "locals" panel.

Another way to trigger this bug:

• Resume the program from the breakpoint.
• When the program crashes, switch to stack frame 2 (AkaoTrack::ReadEvent).
• Enter (AkaoSeq *)parentSeq into the watch panel, and attempt to expand it.
• The same error will occur, and you can see the true value of this variable by double-clicking the missing values and clicking out.

I recorded my debug logs at https://gist.github.com/nyanpasu64/f93591cf7bae02474a4dcb7ed6f3608e. Note that there are a lot of the following error appearing. This may be because of https://bugreports.qt.io/browse/QTCREATORBUG-16890 and https://bugreports.qt.io/browse/QTCREATORBUG-18287 .

         ***    Either you specified an unqualified symbol, or your debugger   ***
         ***    doesn't have full symbol information.  Unqualified symbol      ***
         ***    resolution is turned off by default. Please either specify a   ***
...truncated

I extracted out the relevant lines of text at https://gist.github.com/nyanpasu64/9036538548851368374441f5736da623. In the first file, I expand this.[VGMSeq].[VGMFile].[VGMContainerItem] and "this" disappears. In the second file, I make this reappear.