If you want the perftrills in mono mode, set them to mono mode: Advanced Page / Advanced Tab / Interval Mode from Poly to Mono (or to Global when Global is already set to mono)
The cello trills work better in poly mode in conjunction with the VIPRO sequenzer stuff, therefor are set to Poly in all of our factory presets and matrices.
By the way, avoid performing trills doing it in a "mono synth keyboard style". Holding one key permanently and altering just the second key.
WIth this kind of performing no alternation of the interval samples are triggered, you are forcing always the same interval (sample out of six).
best
Herb