This isn't something Start11 can alter, whilst it would paint the icon for the taskbar when in enhanced taskbar mode (and only enhanced taskbar mode), it never paints the icon on the jumplist or provides the jumplist functionality.
There are three possible reasons I can see :
1) Icon Cache corruption causing the OS to return the wrong icon to things that ask for it
2) You have created a shortcut to Teams which is using that icon.
3) A teams update (which happen often) went wrong.
None of these will be being caused by Start11 itself.
Personally I would lean towards number 3 given how it acts oddly. I would recommend uninstalling Teams and then reinstalling it.