[woodcote]

If I've got this right...

• Both cars are driving round the track okay when the app is in use (green light on powerbase) and when it is not connected (red/orange light).
  
• Both cars change lanes okay?
  
• One car counts laps no problem in the app, the other doesn't count laps.
  

Lap counting in ARC Pro depends on some hardware and some software factors - my hunch is it's how you have the app set up (ie software). It's all here: slotracer.online/arc-pro-guide/preparation

Just for info, which two cars do you have with the set? And which car counts laps and which car doesn't?