Thanks for the update maybe I’m a bit oldschool and need to dig deeper “in the flock” ;-)

Could you just save the pid of that cronjob in a file? (Assuming this cronjob calls bash script). Before the next run of the cronjob check if that process with that pid is still running? Hoping, I understand your problem correctly. You do not want to run the cronjob again until the first run finishes?