The problem I think may be with an interaction between kdocker and "Session Restore" settings, when on KDE Plasma the system is set to re-launch the programs that were running at logout:

I also want to start a program (blueman-manager) minimized to dock (more than that, I need its window open, but docked, in order to fix this odd problem: a bluedevil bug in fact) and I can do it with a much more simple script, which only contains the line kdocker blueman-manager.

That, as well as more complex scripts, like yours, were resulring in the problem you described, until I have disabled that option.

I have noticed that after adding the login script the problem was absent at first logout/login because krunner was not yet running at logout. At nect logout it was running, and was thus "reastored" at login, resultin in a supplementary kdocker process running on top of your script.

The problem might be with an interaction between kdocker and "Session Restore" settings, when on KDE Plasma the system is set to re-launch the programs that were running at logout.

I have noticed that after adding the login script the problem was absent at first logout/login because krunner was not yet running at logout. At next logout it was running, and was thus "restored" at login, resulting in a supplementary kdocker process running on top of your script.

(I also want to start a program (blueman-manager) minimized to dock (more than that, I need its window open, but docked, in order to fix this odd problem: a bluedevil bug in fact) and I can do it with a much more simple script, which only contains the line kdocker blueman-manager. My script, as well as more complex scripts, like yours, were having the problem you described, until I have disabled that option.)

Another solution (in case you must use the option to restore your session) is to add kdocker to a list of exceptions when session is restored.