Have you recently installed other extensions? There are some which are known to conflict with HubSpot.
HubSpot has compiled some steps for troubleshooting tracking issues here. I’d recommend going through these one by one and checking if the issue persists.
@karstenkoehler , wondering if you could lend me a hand. My email tracking stopped working a few days ago. I’m using the Google Chrome plugin. I don’t have any other Chrome plugins installed other than Grammarly. HubSpot is still tracking my old emails. But when I check the tracking box when I’m composing a new email it’s not tracking. I also tried uninstalling and re-installing the plugin.