I think if you were getting SSSS a number of times in a row, it might be worth making contact with the TSA and seeking a redress number.
It may be that you have the same name as someone on a 'list'.
The other possibility is that recent travel to other countries has led to your details being highlighted.

I travel to the US fairly regularly and have Global Entry and still over the past year I have had SSSS on 2 occasions.
Both occasions seemed to be related to somewhat expensive tickets that were bought with <1 week's notice (at least 1 was full-fare F), so that may be related.
In the days before Group 0 it was a relatively pleasant way to get boarded early, at least on BA flights.
I wouldn't worry about it at all, OP.