Background story:
She was delivered from Aker BrattvĂĄg Shipyard in 2003 as Seaway Petrel:
I’ve worked in a ton of drydocks over the years, and this has always been my nightmare.
How the heck does this happen? Not following the blocking plan? Or…?
From the article in Edinburgh Live:
Any word on what the US Navy wanted the ship for?
Are they going looking for old wrecks, or do they have a more “sinister” role in mind?
To protect vital underwater infrastructure . That is “Sal” opinion.
My hunch , they are going to make more " pipe wrecks "
For what it’s worth, here’s the posting today in the US Naval Institute Daily Newsletter. Not an “official” voice, but their reporters generally get very good access to information from the Navy. Includes some comments about the uses the Navy intends to put the ship to as well as the publicly stated intended uses of a UK RN sister or similar ship. The accompanying photo is VERY distressing to say the least!! 
https://news.usni.org/2023/03/27/u-s-navy-officials-heading-to-scotland-to-investigate-r-v-petrel-dry-dock-incident?utm_source=USNI+News&utm_campaign=ebf1dd5f87-USNI_NEWS_DAILY&utm_medium=email&utm_term=0_0dd4a1450b-ebf1dd5f87-230939125&mc_cid=ebf1dd5f87&mc_eid=66eed95f16
Now it couldn’t be sabotage, now could it ?
Gravity
Docking plan - check
Block inspection, including condition of blocks in addition to qty, size, spacing, location according to plan - check
Docking meeting with dock master, including procedures to be used to ensure ship is in proper location during going dry - check
(Ship falls)
Consultants - check
Lawyers - check
Accountability-?
There are very few horizontal supports on port and some of them are wood, I wonder what stb looked like?
This seems like the more dynamic, time constrained situation from that list.
Yes that is what should be the routine before and during docking, with both Owner’s Rep. and Consultant/Warranty Surveyor in attendance.
Been there, done that, in both positions.
Whether that was the procedure followed here we will probably never know.
Edinburgh Shipyard and the graving dock are very old and similar to the docks at the old Keppel Shipyard in Telok Blangah:
Wooden side chocks were used until the end.
The draft required to clear the sill and trim requested by the dock master being agreed to my own experience is that even old yards use divers for this step along with possibly some taut lines stretched across the dry dock for rough positioning. Then judicious use of warping winches / capstans to get things just right. Even during pumping the divers will make final checks until all landed. Yes it can eat up time but pumping is usually slow anyway. Not saying this was even a remote cause in this case. More likely bottom block placement and/or condition. If you are relying on that side shoring to hold up the ship it sounds like you are improvising a docking plan as opposed to following one that was engineered and delivered with the ship.
OM, FYI the old dock has only just been built over after years of just sitting there.
Now that you mention it I recall hearing the divers report the distance the keel is from the blocks as the water is pumped out.
It is using a technique that has been used in graving docks for centuries. In this case it appears there was insufficient propping in place for who knows what reason.
The vessel shifting weights such as ballast or fuel might be another possibility.