hidden simulator errors

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Application: KiCad
Version: 5.1.4, release build
Libraries:
    wxWidgets 3.0.4
    libcurl/7.67.0 OpenSSL/1.1.1d zlib/1.2.11 libidn2/2.2.0 libpsl/0.21.0 (+libidn2/2.2.0) libssh2/1.9.0 nghttp2/1.39.2
Platform: Linux 5.3.11-1-MANJARO x86_64, 64 bit, Little endian, wxGTK
Build Info:
    wxWidgets: 3.0.4 (wchar_t,wx containers,compatible with 2.8) GTK+ 3.24
    Boost: 1.71.0
    OpenCASCADE Technology: 7.4.0
    Curl: 7.66.0
    Compiler: GCC 9.2.0 with C++ ABI 1013

Build settings:
    USE_WX_GRAPHICS_CONTEXT=OFF
    USE_WX_OVERLAY=ON
    KICAD_SCRIPTING=ON
    KICAD_SCRIPTING_MODULES=ON
    KICAD_SCRIPTING_PYTHON3=ON
    KICAD_SCRIPTING_WXPYTHON=ON
    KICAD_SCRIPTING_WXPYTHON_PHOENIX=ON
    KICAD_SCRIPTING_ACTION_MENU=ON
    BUILD_GITHUB_PLUGIN=ON
    KICAD_USE_OCE=OFF
    KICAD_USE_OCC=ON
    KICAD_SPICE=ON

Please add the description of how to recreate the error you are observing.

I had to translate the project from LTSpice to KiCAD. I was not aware that an error will remove the project link from KiCAD to ngSPICE and I lost quite a bit of time because of this hidden error. I had to close the whole workbench and re-open the project in order to simulate with the real circuit after changes.
Next time I will work on a similar project I will save the intermediary project stage and post it here with instructions to replicate the bug.

KiCad bug tracker has moved to Gitlab. This report is now available here: https://gitlab.com/kicad/code/kicad/-/issues/2599