Appium cannot get the webview content when the 'app' capabilities is null

I use appium to test wechat application, when I set the ‘app’ capabilities with a real path, appium can get the webview’s content so that I can find the element, but when the ‘app’ capabilties is null, appium can not find the element in webview. The problem is that when I set the ‘app’ capbilities, the application will be reinstall each time, and the data will be clear too.
I vender why the webview content disappear if I did not reinstall app. and how can I get the webview and not need to reinstall the application.
more info: the content is more when I set the ‘app’ capability in the response of GET /wd/hub/session/7bb68a3a-6213-490b-8154-56988240fe47/source

@dawei1208 correct your driver start capabilities to avoid reset. check -> Different capabilities for different scenarios