Comment 2 for bug 1661233

What I can imagine is that for whatever reason, it takes more time for "less" to scroll by a page than the keyboard repeat interval. Then if you press and hold PageDown, more and more occurrences of it will cumulate in the keyboard buffer, without "less" being able to catch up and empty them.

VTE is very fast in handling less's output and rendering a pageful of data, so I can't imagine this being the bottleneck. Probably the disk is slow ("less" is waiting for reading the contents), or "less" is problematic in some other way, or all of this happens over a slow network connection. If so, there's nothing VTE or Terminator could or should do about it.