Could you provide a test case to indicate which situation will cause the bug?

first time:
route: {
plugin_config_id=1
}
plugin_config: {
id=1,
plugins={
NAME: {...}
}
}
second time update the plugin_config:
route: not change
plugin_config: {
id=1,
plugins={}
}

then the NAME plugin will exist always for route, unless you reload apisix

Good, I can confirm it with the test.