I made a custom dehacked monster for my map, which uses A_AddFlags and A_RemoveFlags mbf21 codepointers to change SHADOW and SHOOTABLE flags, making and arch-vile that is only visible and damageable during resurrection animation. During chase loop, it is supposed to be invisible (spectre-blurred) and invulnerable.
On GZD 4.7.1, flipping the SHOOTABLE flag works as expected, but flipping SHADOW doesn't - the monster remains permanently invisible.
Attaching minimal replication scenario map with 1 custom vile and zombiemen to kill/res.
Correct behaviour can be observed on dsda-doom, Woof, Odamex, DelphiDoom. Example video with expected behaviour on dsda-doom (timestamped)