Hangs (freezes) and becomes unresponsive when moving windows while module using SendToModule is active

My whole desktop consistently hangs (freezes) for about 10 seconds when opening specific programs and quickly start to move them with my current config. I have noticed that the freezing stops occuring if I remove the use of my custom module which sends the time to an fvwmscript which displays the time. It sends the time using SendToModule.

Is FvwmScript responsible for the hang or is the use of SendToModule responsible for the hang, when combined with moving a newly opened window?
I would assume this is because some things are handled synchronously, which in turn pauses everything else until it has finished. Is this assumption correct or not?