Hi @Bombadil,
After a couple of weeks of back-and-forth with HubSpot support, I’ve now got Outlook working at full speed again… albeit by installing the legacy add-in!
I’d noticed there was a constant flickering busy cursor while composing emails with the Office 365 add-in enabled and the HubSpot sidebar open.
Here’s my latest support email:
"…after further research and checking internally, it looks like this may be a clash between your setup and the way that the Outlook 365 add-in sets up tracking in the background. As the tracking constantly scans to find the invisible tracking pixel in the email, even though most configurations will not see an issue, it can definitely cause issues like we are seeing here.
In this instance, we do think it may be better to switch from the Outlook 365 add-in and go to the Outlook desktop add-in as this will track the email in a different way and wont show issues in the compose as we are seeing here.
Here’s some more instruction on how to uninstall the O365 add-in ( Link ) and how to install the Outlook desktop add-in ( Link )"
I’ve re-installed the old add-in (which I used for over a year with no issues) and, unsurprisingly, it’s all much better now.
Please give this a go and let me know if it helps you, too!