There's some dropdown menus within messaging trigerred from an ellipsis icon in the top right.
When you click them, they drop down, and the JS we use tries to automatically position them based on available space and hints given in the code as to what we'd prefer for that dropdown.
Some have some old code, using pull-right or float-right, when they probably should use dropdown-menu-right to get the menu to line up to the right of the button trigger.
In certain weird circumstances, the JS gets confused and the menu is positioned partly off the screen, sometimes it slowly slides back onto the screen eventually. I believe this is the JS doing it's best to position the menu so that it lines up on the left and sometimes getting it wrong. We should use the correct class to tell it to line up on the right hand side for these dropdowns, which solves this problem and makes life easier for the JS library.
86: <div id="conversation-actions-menu" class="dropdown-menu float-right" role="menu"
80: <div id="conversation-actions-menu" class="dropdown-menu float-right" role="menu"
79: <div class="dropdown-menu pull-right">