I've seen this on the Yoga 11e Chromebook, in "tablet" mode (keyboard folded away), and with the Windows 10 tablet. Steps to reproduce: 1. Start a session 2. Bring out keyboard to decrease screen size without resizing session 3. Grab the control bar and drag it up to reach the bottom half of the session 4. Click and drag the desktop to see touch events happen *not* beneath your fingers, but offset by approximately the amount you scrolled.
This works for me with ThinLinc 4.10.1 (eudemo) and Chromebook 77 and Chrome 77 (on Windows). I guess it got fixed with bug 6132.