UIAutomator2 not identifying mobile element whereas UIAutomator does

Post upgrade of our Android devices to OREO, our execution became terribly slow so i switched to UIautomator2.
But some elements which were getting identified through UIAutomator are not getting identified through UIAutomator2.

Should something be done in the apk under test.

By the way when upgraded from Android 7.0.0 to Android 8.0.0 the execution time increased x4 times.

Appium server: 1.8.1
Appium java-client: 6.0.0