the settle setting should solve the star trails, i will let you know. I haven't notice it before as its default value works well before.
About the Zoom issue, i have tested it just a minute ago with a config (Canon DSLR, QHY guide camera and Simulated mount). Obviously, the plate solving does not work by day (in france), but i can zoom in and out as with version 3.5.4. The issue here occurs after a successful plate solving in the PA process, during every 3 or 4 nights since i have updated to 3.5.5. Tonight, the weather might be clear enough to give a shot on that issue, but will go worse and worse in the night (bad enough to make astrophotography not possible). Maybe tomorrow evening but not sure as the forecast in the next days are cloudy and rainny in western France.