End of wits reached: set-path with regsub just doesn't work

This should be pretty simple, right? HAProxy version 1.8.23.

    http-request set-path %[path,regsub(/apache1/,/)]

That would take the path /apache1/status and change it to /status? I just doesn’t work. If I put in a hard-coded path like http-request set-path /status then it’s OK. That works.

How do I debug this? The environment I’m in is very paranoid, so I can’t see the backend server’s log nor can I do a packet capture. I have tried various hacks to get the resulting path into the logfile, but none of them work either.