suppose -> in t0 you had 120 tables
in t1 you run segment advisor and it did 80 recommendations
in t2 you dropped half of those tables
in t3 you run segment advisor and it did 40 recommendations :)
Something like this may even be the cause.
That is why, send me the recommendations and object names , so I can comment. (for both of the cases)
Segment Advisor Recommendations Showing Non-Existing Tables (Doc ID 456616.1)
Segment Advisor Recommendation does not get cleaned After Implementing it (Doc ID 1540915.1)