After 30 days one of the traits in our account always looses all of its reach, which results in us repopulating it from the LiveRamp side. There is a setting for this in the Adobe Audience Manager regarding audience invalidation, but the maximum amount of days is 30.
It seems like you are ingesting Trait data via Live Ramp via 2nd/3rd party data onboarding, If thats the case then you can ask Liveramp team to change the TTL of that particular trait.
If thats not the case & data is coming from your own website then you can change the TTL itself by editing the properties of that particular trait.