BBC Iplayer constantly buffering

I’ve been using BBC Iplayer add-on for a long time without issues. A few days it started buffering every 30 seconds making everything unwatchable.

I uninstalled the add-on and said to remove all data. But when I re-installed it the add-on remembered the last programme I watched, so I assume not all data was removed.

Other streaming services and video files play fine with no buffering. I can also use BBC iPlayer on Kodi on my main PC with no buffering.

How do I completely remove all BBC iPlayer data and reset it back to a completely new installation?