Android app only works on android 7.0+ others show white screen after splash

Im working on a project with ionic(v4)+angular+angular material. Im trying to export apk but i have a problem. i tried several emulators for testing. But i got white screen after splash screen on android 4.4, 5.0 and 6.0. But it also works well on android 7, 8, 9. my config.xml has these line;

<preference name="android-minSdkVersion" value="19" />

downloaded sdk 19 with android studio.
removed android platform and installed again for several times.
Please help me if you know any solution. If you need to know anything about project just ask me.

This seems to be an issue stemming from Ionic 4’s usage of ES2015 syntax which isn’t supported by older versions of webview, see e.g.

Part of the problem is that on old emulators (as opposed to actual devices) webview doesn’t get updated, so whether it runs on the emulator is not necessarily indicative of whether it runs on the actual device. Unfortunately I haven’t seen any reliable information regarding which versions it will actually work on. I have an old 4.4 tablet lying around where I couldn’t get it to work. 5+ might work if you install but I can’t currently confirm.