Strange issue with macOS 10.15. and broken pipe

[MartinBuchmann]

I am sorry for bothering you but I just don't know where to ask. I am using some foreign CL code to create an animation using external-program to pipe cairo surfaces into an ffmpeg process which was started using external-program:start.

While on macOS 10.13. everything is working on 10.15. I get the following error:

Couldn't write to #<SB-SYS:FD-STREAM for "descriptor 15" {1001A962D3}>:
  Broken pipe

I am using SBCL 1.5.9. on both machines, ffmpeg is installed properly via macports and the process is :RUNNING according to external-program:process-status. I assume, that there was some change in the inter process communication or security settings but wasn't able to debug this further. Is anyone using macOS here and can confirm the issue?

Any hint will be gratefully appreciated!