Spiders and cave spiders no longer flee from armadillos.
I previously conflated this bug with MCPE-178560 as they were relatively similar and both introduced in 1.20.70.21, but while that has now been fixed and spiders again counterattack mobs and players, they still do not flee from armadillos. The reason for the regression may potentially be similar, however.
Comments 2
The "Update 1.21" and "Armadillo and Wolf Armor Experiments" use different versions of the spider and cave spider behavior json files. When you activate both experiments, one file will overwrite the other. That may be intended because that's how addons work and it is not possible to automatically merge these files.
Do note that this only happens when you also enabling "Update 1.21" experimental toggle, alongside the "Armadillo and Wolf Armor" experimental toggle.