To reproduce:
1. Open any 2 Unity apks;
2. Make one of them to be a floating window (on Samsung devices, you can go to Tasks > Press and hold on one of the Unity apks > Drag it to a box that says: "Drop here for pop-up view");
3. Try to rotate the device.

Expected result: Both apks rotate when device is rotated.
Actual result: Apks don't rotate when device is rotated.

Note: sometimes locking and unlocking the device solves the issue.

Tested with 2 non-Unity apks, 1 Unity apk and 1 non-Unity apk, the issue does not reproduce.

Reproduced with 2019.1.6f1, 2019.2.0b6, 2019.3.0a5.

Devices under testing:
Reproduced with:
VLNQA00149, SAMSUNG SM-G960F, Exynos 9 Series 9810, Mali-G72, 9.0.0
VLNQA00219, SAMSUNG SM-N960U, Snapdragon 845 SDM845, Adreno (TM) 630, 8.1.0
VLNQA00150, SAMSUNG SM-G960U, Snapdragon 845 SDM845, Adreno (TM) 630, 8.0.0
VLNQA00263, GOOGLE Pixel 3, Snapdragon 845, Adreno (TM) 630, 9.0.0
VLNQA00276, Asus ROG Phone, Snapdragon 845, Adreno (TM) 630, 8.1.0
VLNQA00271, SAMSUNG SM-F900F, Snapdragon 855, Adreno (TM) 640, 9.0.0 (foldable device).