I'm specifically on about Grove Cliff Fissure which is accessed further along the cliff line a few metres from Rumble Chasm. We connected those two to Skittle Alley in 2018 / 2019. Clearly neither had been visited in a long while and certainly never frequently. Having spoken to Nigel about them I suspect the number of visits prior to 2018 could be counted on one hand. Loose stuff all over the place and very little evidence of people having been in. The difference compared to the well visited rifts of Flagpole, Skittle Alley and Guano was very stark. As you say those were heavily used in 80's, 90's and 00's and are consequently fairly free of loose rock unless you go looking for it.
I've no doubt the rifts remain active (bits of the cliff regularly fall off) but footfall seems to have cleaned things up far quicker than geological processes can create new loose stuff. I can't think I've ever seen evidence of 'new' loose stuff, rather remaining choss that nobody had so far touched.
Last summer we noticed a few loose bits had fallen from the roof of Hopeless near the entrance. A week or so beforehand the climbers had reported some movement on the cliff outside. Despite this my betting was on somebody twatting the ceiling with their helmet and dislodging something that wasn't as stable as it perhaps looked. Who knows really. I've certainly seen evidence of the caves throwing stones, but compared to human aided movement personally I think it's very rare once the initial loose stuff after discovery has dropped. That time period is obviously foot fall dependent.
There was of course the total b*****ks about a loose boulder in Flagpole around the mid 00's which led to the end of outdoor education groups using the cave.
