I just created a game. I set it up as the default settings, except SM Race.
Generated about 8-9 systems before I found one I liked. Created a SM Race colony on the planet to change the atmosphere. Deleted the SM Race colony when I was done. Then I created an empire using the Create Empire button off the F9 screen.
After 3 years, there was one interruption with a potential interrupt. That lasted for 26 seconds (game time) and less than that real time. My survey ships have 120m km active sensors ON, so anything in the system or the neighboring system should have been found, or at least be curious. The survey ships ran out of fuel surveying the second system, but nothing was found there yet either.
Did you delete the SM Race colony after you were done with it?
And it's possible it could entirely be just bad luck on your part.