Hi @mazeyrat,
I talked with one of the developers and we think that this is the same underlying issue as the bug mentioned in your other post: [BUG-13990] Ignition 8.0.2-2019-05-09 - designer freeze when creating an UDT instance
I don’t have a ETA for that ticket, but it is high on our list. I will let you know when its fixed so you can see if that fixes this issue as well.