Scheduler Jobs are not distributed according to OS-load on RAC noes

Every hour we are scheduling a lot of one-time jobs to run a lot of data loads. The Jobs are scheduled by a master which takes care of dependencies - so a job is only scheduled, when all it dependencies are met and should run as soon as resources (job processes) are available. (No dependencies are defined in dbms-scheduler framework). The jobs use a JOB_CLASS which as a dedicated SERVICE - this SERVICE is available on all 4 instances. Stop&Start of the service on the "idle" instance does not help.
NTP is fine according to cluvfy comp clocksync -n all . instance_stickiness
<https://docs.oracle.com/en/database/oracle/oracle-database/18/arpls/DBMS_SCHEDULER.html#GUID-D7A11F8A-8746-4815-91C4-BC8DDBA4C74A>
is
TRUE (the default) - but I don't think this will change anything as our jobs run one-time only.

Does anyone know how to identify, why sometimes some instances refuse to run scheduled jobs?
Who is doing this decision, and can it be traced somehow to identify based on which numbers the decision is done?
Any other suggestions?

A SR at MOs is open, but without any progress.

related documents found so far:

DBMS_SCHEDULER job doesn't fail-over across RAC instance ( Doc ID 2365434.1
<https://support.oracle.com/epmos/faces/DocContentDisplay?id=2365434.1> )
RAC Node X Is Seeing A Higher Session Load Than The Other Nodes For Scheduler Jobs ( Doc ID 1602581.1
<https://support.oracle.com/epmos/faces/DocContentDisplay?id=1602581.1> )
ENH 28592547 <https://support.oracle.com/epmos/faces/BugDisplay?id=28592547>- REAL-TIME LOAD BALANCING FOR JOBS ACROSS RAC INSTANCES

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