Sub Process not showing when reaching the Call Activity

Hi everyone.
I'm very new to Bonita, so any help is appreciated!

So I am using a Call Activity in my Main process to call a Sub Process. However, for some reason the sub process is not showing when I reach the call activity and just ends the process there, ignoring the rest of the process.

I was able to get the sub process to display yesterday, by starting a project from scratch. But as soon as I add the Data to be sent and received via the sub, it started disappearing again.

This morning I rechecked and the sub process is again disappearing, even without the data sending portion.

Both Main and Sub Processes have a start activity and have Walter Bates assigned as the user.

Any advice on why the sub process keeps disappearing and what I can do to fix that, please?

Thank you!