Writhing Invitation does not drop (Eater miniboss)

Report# 1,016,857,445
Report# 63,032,911 < see edit 3

Writhing Invitation does not drop. Running Eater influence in a t14 map, white map no map mods, map randomly is assigned shaper influence. On killing the map boss no invitation drop, map shows as complete, Eater counter shows 14/28 as of completing this map. I think shaper showed up right when I was about to finish the boss and gave me a cutscene, but that could have been one of the previous two maps. I ran around looking for unique shaper mobs that sometimes spawn on the boss and killed one elsewhere on the map, no luck. On opening the next map the Eater count went up to 15. Killed that boss, no invite, count stayed at 15 as you'd expect.

I'm sure I've missed multiple invitations for this miniboss over the last day or so, like 3-4 so far. I just thought I was missing count of which map I was on and the count was at 15 next time I looked with no invite. But now I think about 50% of my miniboss invites haven't dropped despite killing the boss.

--- EDIT ---

I do *not* have "Etched by Acid", the atlas tree notable that gives a 10% chance for double progress towards the Eater of Worlds. Someone was probably going to ask that.

Also ran this with one fragment - a betrayal scarab (your map contains Jun).

--- EDIT 2 ---

After getting to 28/28, the Screaming Invitation did not drop on map 28, it dropped on the "29th" map. So the counter ticks from 27/28 to 28/28 when the eater mobs spawn in with that flash of blue light, and iirc that's supposed to be the map where the eater invite drops, if you kill the map boss which I did. No invite. The counter stayed at 28/28 on the next map, and that map boss dropped the invite. This has also happened multiple times this league. I think it's worth mentioning - the counter maybe was off for most of the 28 cycle, for some reason, and maybe that's related to one or both of the invites not dropping when I expected.

--- EDIT 3 ---

Report# 63,032,911

Watched it happen again. Counter at 13 after spawning eater influence, defeated the boss just to confirm, no invite (which you'd expect). Back in hideout I checked before opening next map, counter was at 14. On spawning eater influence in this map counter advanced to 15. White map with no scarabs or other frags, no atlas passive for 10% chance of extra progress, this time no shaper influence.

After playing more, I'm seeing that when you go into the mirage of a map with exarch/eater influence, you advance an extra turn of progress when you spawn in the red/blue mobs inside the mirage zone. I guess I missed this interaction at league start, but if that's what caused the previous progress skips for me, that's a pretty good reason why it would have happened. I don't think that clears it up for me entirely, but I may have just derped all those maps.

On the plus side you can get 2x turns of progress per map now if you're hunting eater/exarch. Also if my counter is at 13/28 after spawning influence in the main map and I don't wanna risk losing the miniboss fight on the next map by forgetting or something (I still need black star for the polaric devastation ring), I can go into mirage and advance the counter to 14, before coming back out of mirage and killing the map boss to get the miniboss invite, when it wouldn't have dropped from the boss if i was still at 13 progress.