Qt 5.13.2 -> Qt 5.14.2 causes fps to drop very low for specific sites

Some of the sites we are using for benchmark tests, shows a very large drop in fps.

Specifically:

http://antutu.com/html5/game.html

http://antutu.com/html5/collision.html

Both had around 35-40 fps in qt 5.13.2 and now 3-4 fps.

They are both part of a testsuite found on

http://antutu.com/html5/

The rest of the tests in that suite performs as good as, or even better than before.

My setup:

The platform used for the tests are an iMX6 based board supplied by Freescale: imx6sabresd evaluation board.

I am using the vivante proprietary OpenGL libs for hardware acceleration.

Building in Yocto, and basing my work on the dunfell release of Yocto and dunfell branch of meta-qt5.

Command used for test:

./simplebrowser http://antutu.com/html5/game.html --no-sandbox --enable-gpu-rasterization --enable-accelerated-2d-canvas

Notes:

1:

I traced it down to work as before ( i.e. as well as with qt 5.13.2) with the chromium 75 browser in commit in qtwebengine.git:

51228eb249a178ada6ebd2ccd5e662bcd7bd2c60

2:

Tried disabling the viz display compositor, which seems to cause no change at all.

3:

What does seem to cause a change is to drop "- -enable-accelerated-2d-canvas" and add "--disable-accelerated-2d-canvas". If I do that, then fps rises from 3-4 to around 20 fps using http://antutu.com/html5/game.html. But disabling the 2d hw accelerated canvas then causes the http://antutu.com/html5/birds.html to drop from around 30 fps to around 2.

4:

Tried the 5.15.0 version of meta-qt5 that uses chromium 80, but I am seeing the same problem as with qt 5.14.2.