One way to deal with the order dependency issue. This is not the best way, more like a proof of concept.

Author: rwgk

include/pybind11/detail/type_caster_base.h

@@ -713,13 +713,28 @@ class type_caster_generic {
             // if we can find an exact match (or, for a simple C++ type, an inherited match); if
             // so, we can safely reinterpret_cast to the relevant pointer.
             if (bases.size() > 1) {
-                for (auto *base : bases) {
-                    if (no_cpp_mi ? PyType_IsSubtype(base->type, typeinfo->type)
-                                  : base->type == typeinfo->type) {
-                        this_.load_value(
-                            reinterpret_cast<instance *>(src.ptr())->get_value_and_holder(base));
-                        return true;
+                type_info *best_base = nullptr;
+                if (no_cpp_mi) {
+                    for (auto *base : bases) {
+                        if (PyType_IsSubtype(base->type, typeinfo->type)) {
+                            if (best_base == nullptr
+                                || PyType_IsSubtype(base->type, best_base->type)) {
+                                best_base = base;
+                            }
+                        }
                     }
+                } else {
+                    for (auto *base : bases) {
+                        if (base->type == typeinfo->type) {
+                            best_base = base;
+                            break;
+                        }
+                    }
+                }
+                if (best_base != nullptr) {
+                    this_.load_value(
+                        reinterpret_cast<instance *>(src.ptr())->get_value_and_holder(best_base));
+                    return true;
                 }
             }