Dropdown with bootstrap 4 - open animation flicker

[krokiet]

Bug description:

Dropdown with bootstrap 4 open animation flickers from time to time. Sometimes it's almost every time and other times it's once every 5-10 clicks.

This issue can be reproduced on official example page: Angular bootstrap dropdowns and it occured on windows and linux using both firefox and chrome.
The last version that appear to work correctly with bootstrap 4 is 5.6.1

Versions of ngx-bootstrap, Angular, and Bootstrap:

ngx-bootstrap: 5.6.2 - 6.2

Angular: 9

Bootstrap: 4

Expected behavior

Dropdown animation shouldn't flicker

[rewgoes]

The same thing happens with Angular 10.

[ahettlin]

And Angular 11

[matejbizjak]

It also happens in version 10.2.0 with Angular 15 and Bootstrap 5.