Thank you for everything!
About the bug of the substitution of a sub-model, you can try with the file I sent you. Go to the page 85 for example where there is a sub-model of a flex, and try to do Right click / Substitute on the bent flex in the PLI (you can also try with a motor page 2). If you don't have any problem, perhaps it's something wrong with my computer / installation of the software and the LDraw library.
About the bug of the substitution of a sub-model, you can try with the file I sent you. Go to the page 85 for example where there is a sub-model of a flex, and try to do Right click / Substitute on the bent flex in the PLI (you can also try with a motor page 2). If you don't have any problem, perhaps it's something wrong with my computer / installation of the software and the LDraw library.