Linear (ramp) change on tempo

Hi there,
On W10…
I would like to know how works Cubase with the tempo : when I have a long session (for example for a feature film) a linear tempo change can’t read correctly : a lot of twitchs so I can’t hear properly the effect even if I have only one instrument playing (performance meter is very high).
If I have a smaller session (for example a short film with a big orchestral session) it works fine.
Why and how can we manage this ?
Thanks for your help