Hi Roadrunner,
Screensaver:
Check your powersaving settings, as some are set on laptops to turn off usb devices when not doing much. If thats not the case contact support via support and they will ask you send a debug file so we can narrow down whats happening.
Aircraft:
Some transponders and data received from aircraft don't always the aircrafts heading (bug in transponders we think). This also may occur when you first have contact with an aircraft and only once more data is received then the heading data is gathered as well. Without the heading data the symbol turns into a circle as we cannot display a aircraft as we don't what its heading is.
Hope that helps.