I have recently experienced sporadic Log & Track on my emails. All my settings are correct - yet some emails pull through and others do not. The contacts are already in my CRM. I use G-suite - my extension is correct and logged in (turned on).
There are some requirements, as documented in our Knowledge Base, for an email to log properly. It’s worth reviewing them just to ensure that everything is connected correctly: Log email replies in the CRM.
The key point that I noticed with questions regarding email logging is that the original email must be sent through the CRM or sent from your connected personal email client with the sales email extension or add-in installed and the Log checkbox selected, otherwise they would not log.
Incoming emails sent to your connected personal email will not log to HubSpot if they do not meet the requirements for logging.