In Aug 2023, a bug in Katalon Studio 8.6.5 was reported. See the following topic. I believe that your issue is the same as this previous incident.
Katalon released v8.6.6 to fix this issue. I checked that v8.6.6 actually fixed it.
However you wrote:
I wouldn’t expect v8.6.9 to reproduce the problem, but you wrote it does. I have no idea why.