Report Cron errors and allow retry
The jobs in queue are just executed one by one without any error checking - Regardless of any errors which may have been occurred while executing a job its removed from queue list and somewhat marked as (successfully) done.
This can be a big issue if any error occur. This could be because of wrong configuration and other permanent errors, but also for temporary errors like insufficient memory (In my case I disabled exec/shell_exec function in CLI php.ini).
Best way would be to have jobs executed in some kind of transaction (e.g via a sandbox) to allow reverting them. I know this would be a huge task and nothing which could be fixed in a day.
But it would be great to be at least able to see that an error occurred directly in the ISPConfig panel. For example if an error occurred during execution of a task, the job could be kept in the queue and marked red with the possibility to see an excerpt from the cron log and a "Retry" button.
This problem makes using ISPConfig a lot more complicated because every time I make an important change in the web panel I have to check the cron log carefully and if I see any problem I don't have the possibility to easily retry the job but have to e.g remove the created site and create it again...