Villagers don't walk on double carpets even though they wouldn't fall. It's kinda handy with trading halls, but pillagers can shoot them and they don't run onto the carpets and just sit there. I found it when I was trying to make a trading hall and notice that they stood next to each other in front of their workstation forever and never moved, as long as they all stood on the carpets. It is a bit broken and I hope this gets fixed anyway (They didn't panic when some pillagers came in, didn't spawn an iron golem and all died