i was perusing the free controls today and noticed, the hover over radzen component example using the duration on the tooltip doesn't appear to close after 10 seconds.
to be fair, it may be an old version, i have not tested on a site, i will do that next.
if i had to guess what it is, i would venture that async is not always async, sometimes you need to force a new thread.
There was an issue with the tooltip which we have fixed. Your application probably used an older version where the issue didn't appear. The latest Radzen.Blazor version should address that problem.
