I did try praising them twice in a row. They stop working and told me to stop nagging...

Once on each of two work cycles?

Hitting praise twice in one work cycle...

Once on each of two work cycles works for me.

Yeah. Twice seems to work all right but three times is too much - they tell me to stop nagging. That's why I try to keep some candy or fruit available; it works as well as the praising glove, but they don't complain about getting it too often, the greedy little whatsits.