If it's not abundantly clear, Linkedin is not in love with tools like Super Send. They do not make it easy on us to provide a lovely experience. Occasionally getting disconnected comes with the territory.
Here are all the possible reasons why your Linkedin account might be getting disconnected frequently from Super Send:
Logging in / out from desktop or mobile
Logging in / out from a new location
Logging in / out of a new profile (perhaps a customer of yours)
Logging in from a new computer
Logging in on the mobile app
Not opening the chrome extension for > 2 weeks
Sending too many messages in a short period of time
Not visiting Linkedin for too long from the chrome profile where the super send extension is loaded
In short, there are 101 ways a Linkedin disconnection can happen.
Log in to Linkedin on the web with just one Linkedin profile in google chrome and then open the super send extension
Don't log out of Linkedin
Visit Linkedin once a week or at least once every two weeks.
Open the super send chrome extension once a week or once every two weeks.