To repro:

add the following to a GML Playground:

@GUI::HorizontalSlider {
    min: 2
}

ASSERTION FAILED: min <= max
../../Userland/Libraries/LibGUI/AbstractSlider.cpp:68

0x30e1f1a8: [libsystem.so]  +0x8 (syscall.cpp:35)
0x684dfc76: [libc.so] __assertion_failed +0x106 (syscall.h:44)
0x67e7b4d1: [libgui.so] GUI::AbstractSlider::set_range(int, int) +0x81 (AbstractSlider.cpp:68)
0x67e7b535: [libgui.so] AK::Function<bool (AK::JsonValue const&)>::CallableWrapper<GUI::AbstractSlider::AbstractSlider(Gfx::Orientation)::{lambda(auto:1&)#4}>::call(AK::JsonValue const&) const +0x55 (Function.h:111)
0x67f6b78d: [libgui.so] GUI::Widget::load_from_json(AK::JsonObject const&, AK::RefPtr<GUI::Widget, AK::RefPtrTraits<GUI::Widget> > (*)(AK::String const&)) +0x1ed (Optional.h:113)
0x67f6c3fc: [libgui.so] GUI::Widget::load_from_json(AK::JsonObject const&, AK::RefPtr<GUI::Widget, AK::RefPtrTraits<GUI::Widget> > (*)(AK::String const&)) +0xe5c (Atomic.h:266)
0x67f6ccb1: [libgui.so] GUI::Widget::load_from_gml(AK::StringView const&, AK::RefPtr<GUI::Widget, AK::RefPtrTraits<GUI::Widget> > (*)(AK::String const&)) +0x81 (Widget.cpp:984)
0x5d90a6c7: [/bin/Playground] AK::Function<void ()>::CallableWrapper<main::{lambda()#1}>::call() const +0x67 (Atomic.h:266)
0x67f453e1: [libgui.so] AK::Function<void (Core::Object&)>::CallableWrapper<GUI::TextEditor::did_change()::{lambda(auto:1&)#1}>::call(Core::Object&) const +0x41 (TextEditor.cpp:1338)
0xad4e3f8a: [libcore.so] Core::EventLoop::pump(Core::EventLoop::WaitMode) +0x37a (Function.h:57)
0xad4e45bb: [libcore.so] Core::EventLoop::exec() +0x4b (EventLoop.cpp:390)
0x67e8b615: [libgui.so] GUI::Application::exec() +0x25 (Application.cpp:121)
0x5d909a0e: [/bin/Playground] main +0xd7e (NonnullRefPtr.h:295)
0x5d90a155: [/bin/Playground] _start +0x45 (crt0_shared.cpp:60)

Seems to affect HorizontalSlider and VerticalSlider.
SpinBox seems fine.