Hi all, if it can be of any help I found out the problem lies in the expression guids of the material instances parents, there appears to be some collisions of IDs between materials expressions and materials functions expressions, leading to the rewrite of parameters names and consequent shuffle of parameters values.
Still not sure how or why this problem arises only when updating to 4.19, maybe a deserialization bug?
I got the materials to render correctly by invalidating the expression guids in the parameters, but the editing is still broken.