The looping has blocking impact on mainloop. Although it has preloaded frames for the start, the loop is not “seamless”. This is not noticable with short stacks of small files like in the help patch but gives huge drops on very big frames. I think basically any stack that is too big or too long to be cached away by the ssd controller.
This seems to be something wrong on my side only and i am not sure what caused the issue, it is gone now. Sorry.