Sorry, I suppose I choose a wrong label; I don't know what label to use. I haven't found a better place to let you know about an issue recently reported to us by an Add-in Express customer. The report is published at https://www.add-in-express.com/forum/read.php?FID=5&TID=15903. We’ve found that the issue is: to show their panes, the two add-ins (Hubspot and Add-in Express) subclass the same window and, since they don’t know about each other, when one of them unsubclasses the window, the other one's pane stops working.
Just to clarify, is the customer experiencing an issue in which the form on the email is appearing twice? Based on the screenshot that customer shared, I'm not 100% sure what's the exact issue is. If you could expand the issue, I'd be more than happy to look into it.
Additionally, what's the outlook and HubSpot extension verison that customer is using? Are they on PC or MAC?
You subclass a window to override the default window procedure. For example, you override the default reaction to the WM_WINDOWPOSCHANGING Windows message – it is sent to the window when it is being resized – so that the resulting window contains two areas: the Outlook content and your pane. Add-in Express does the same.
Now, because two add-ins don’t know about each other, the second subclasser receives the coordinates of the modified window, not the coordinates of the original Outlook window. This causes the second subclasser to place its pane in a wrong location.
This issue may relate to the order of subclassing. The user can change this order by turning the first add-in off and then on. That means you can see the issue on your side if you install an Add-in Express add-in; I can provide a test add-in if required.
What you see in that screenshot are two images created by the same Add-in Express pane instance; Add-in Express embeds the pane in the above-described way. One of the images is alive: the pane controls it even though the coordinates used are incorrect. The other image is dead: it reflects the previous location and state of the pane and it doesn’t redraw.