When testing with PHP 8, I was wondering why I was seeing so many errors in the matomo.log like

WARNING Ecommerce[2020-08-17 15:42:06 UTC] [56b55] /home/lukas/public_html/matomophp8/core/Plugin/Report.php(924): Warning - Undefined array key "items"

that when taking a closer look should be silenced with an @.

It turns out that https://github.com/php/php-src/pull/3685 caused a change:

Error handlers that want to only handle non-silenced errors may have to be adjusted. A common pattern I found in our own tests if checks for error_reporting() != 0 to detect silencing. This should be changed to error_reporting() & $err_no to detect whether the specific error type is silenced.