You are right about some instabilities with the panels... It's possible that the change from GTK2 to GTK3 has introduced several bugs that have not yet been solved. Depending the theme you choose, your mileage may vary.
The Dock applet is currently in version 0.87 but we get 0.85 from the 18.04 repos.
I installed that version following the instructions in the link that I put in the following post and it seems that many problems are solved:
Let's hope this issues are solved ASAP.