Please note I have checked the change log and this is under experimental features and is not current vanilla game play. I do not have experimental features turned on.
Villagers are no longer lowering trades after 2nd infection. As per the change log, this should be an experimental feature and I cannot see where it has been added to the main game.
This change is not under the "Experimental Features" section in the changelog. It is under the "Fixes and Changes" section. Resolving the report as a duplicate of MCPE-176506.