Crontab launched GUI is unable to successfully launch processes

Question

I have in house GUI tools written in c++. These programs are often capable of launching some other (c++) GUI. The way the process launching happens is via the classic fork, if it might matter.

There are never any issues, unless I launch via crontab, in which case all of the process will always fail in spawning the children. To be precise, I can see the children being defunct as soon as I try to start it.

Note that launching from crontab does not prevent the process from working correctly, it simply causes their forked children used to launch other GUIs to immediately go defunct.

I have been unable to understand the root cause of the issue. I've tried specifying DISPLAY on the crontab line launching the GUI, and the crontabs start with 'BASH_ENV=' so the environment inherited when launching via cron is the same as the one provided when manually launching the GUI.

I am running redhat6 and fvwm as window manager.