Detailed logs are on and my FR5 diagnostic display stalls when its folder is busy; separate cell controls are unaffected, but I haven't separated communication time from file-write time in this replay bench.
I had a viewer do this when every received line waited for a file flush. Time receive, enqueue, write and display separately with the same replay. A queued writer can help, but give it a bound and an explicit overflow policy so a stalled disk doesn't merely turn into growing memory use.