Memory thread feedback request (can't find any)

Hi,
Ever since I completed the first three memory threads and killed the incarnations, I've never encountered a memory thread. I am starting to think I am missing a quest checkpoint or something because I feel locked out of this content.
I get that they are probably rare (like the seer?) but I need at least some reassurance from players who have been able to find some because I have found almost nothing on the topic.

a) Is there a step between getting a darker atlas board with petals and finding new memories ?

b) Can they be found only in memories influenced map ?
c) Average rate encounter ?

d) Any other info will be appreciated.

IIRC they are only found in T16 maps and are pretty rare - like every 10+ normal maps.

ive burned full 20 stack of scarabs and found just one thread

I must be really lucky then. I finished a thread of maps then next T16 I had memory lol

Same issue, probably done 20-30 T16's after the "quest" memory strands, not seen a single one... Almost feels like standard league at this point

Ok I've finally encountered a memory tear.

The only thing I did differently than before is I disabled Delirium from my maps. Before than I always had a Delirium Mirror (100% chance).

I honestly doubt that spawning a mirror is preventing the spawn of a memory tear, but I am happy enough that I am going to keep it this way.

If anyone has been able to find a Memory Tear in a map with a Mirror of Delirium, please let me know because I love this mechanic.

60+ t16s after finishing the questline and not a single memory tear yet, and that's with the 40% increased chance from the atlas tree. They could have made the memory threads shorter (I heard they are 4 to 8 maps long after the quest) but a lot more common, because this feels particularly awful if you do longer maps with slower mechanics, dip into non-atlas content, etc. Add more modifiers after each map to make up for shorter threads, split the echoes into fragments if they don't want easier access to the new pinnacles, these details are not hard to solve either. Gating the new content this heavily behind RNG is honestly baffling.