I have a flow which always runs fine.
After adding a tool to a branch that should only process one filtered record, the flow got stuck in “In Progress” for several hours.
I am not sure if this was a one-off issue, because I cannot test it further in this environment. However, my gut feeling is that it was related to the tool, because this had never happened before and only started after the tool was added.
On the tool output, I had a script pointing to a non-existing function. I expected this to return an error, but instead the flow remained stuck in progress.