Code change:
The RTT for a network path may change over time.  If a path's actual RTT decreases, the min_rtt will adapt immediately on the first low <del> sample.  If the path's actual RTT increases, the min_rtt will not adapt to it, allowing future RTT samples that are smaller than the new RTT to be included in smoothed_rtt. </del> <ins> sample.  If the path's actual RTT increases however, the min_rtt will not adapt to it, allowing future RTT samples that are smaller than the new RTT to be included in smoothed_rtt. Endpoints SHOULD set the min_rtt to the newest RTT sample after persistent congestion is established.  This is to allow a connection to reset its estimate of min_rtt and smoothed_rtt (smoothed-rtt) after a disruptive network event, and because it is possible that an increase in path delay resulted in persistent congestion being incorrectly declared. Endpoints MAY re-establish the min_rtt at other times in the connection, such as when traffic volume is low and an acknowledgement is received with a low acknowledgement delay.  Implementations SHOULD NOT refresh the min_rtt value too often, since the actual minimum RTT of the path is not frequently observable. </ins> 5.3.

Related discussion:
text: If we are to suggest that an endpoint MAY reset minrtt when persistent congestion is declared, I think we should consider the risk of not having good estimate of minrtt, as we would have during the handshake.
I don't see that as a risk here. min_rtt doesn't consider any discretionary delays.
NAME That's exactly the problem. will be inflated by , unless and until the peer sends an immediate acknowledgement. And until that happens, will as well.
I think that's OK. In practice, immediate ACKs do happen, and even at low rates, this should resolve to a "true" minimum. And if it doesn't, then you have worse performance than you might had otherwise. You have to have a pretty poor network (or a terrible ACK generation regime) for minrtt not to eventually resolve to a useful minimum. Explaining this risk is fine, but the endpoint that does this made the choice to throw out minrtt and that's just a consequence of that.
On one hand I agree that we can expect to see immediate ACKs, especially when HTTP/3 is used. At the same time, I am not sure if resetting minrtt when observing persistent congestion is better than other cases where we might reset minrtt, but that we do not currently mention. Change of IPTTL could be one of the examples in this regard (IIRC NAME pointed out that we do not use that value for detecting path changes). To summarize, I think talking about resetting minrtt might be fine, though I am not sure if that discussion should be tied to persistent congestion.
To give a specific example, one problem that I know with the current definition of minrtt is that it cannot detect and correct RTT estimate of a congested path. The sole purpose of minrtt is to discard excessive ack-delays being reported by the receiver. This works by capping the lower bound of adjustedrtt to minrtt. The problem here is that minrtt is a value that is typically collected when the path is almost idle. Once the path becomes congested, the true RTT becomes much greater than minrtt.