cannot dock dockwidget that was previously docked

i have exactly the same issue as this post from 2010

https://forum.qt.io/topic/680/qdockwidget-will-not-go-from-floating-back-to-the-docked-state-why

I have an application in a mainwindow, i have several dockwidgets docked on TOP, bottom, left, right .. i start with the mainwindow as small as it can be given the objects inside it .. I drag one out from the window and i cannot dock it again, unless i make the mainwindow larger .. this is a serious issue for me .. i even tried on click making the dockwidget extremely small, even so, it cannot be docked when there is clearly enough room .. what is the solution?  it does not matter if there is anything docked there either .. so if i drag a dockwidget from left position, leaving NONE left docked there even then i cannot dock it, unless i make the height of the mainwindow larger ... need a solution for this critical issue - Note that i would love to have a solution/workaround that i can use now in the current Qt ver we are using 5.15.2