Partly that’s deliberate.
The severe problems at the start of the Astute programme - leading to the Electric Boat Company having to step in to provide assistance - were largely attributed to the run down and virtual disappearance of all trained staff due to the 10 year hiatus after the delivery of the last of Trafalgar class, HMS Triumph, in 1991, to the first of the Astute class being laid down in 2001.
An outcome was the decision to spread construction in future so that the transition from Astute to Dreadnaught, and to what was then SSN-R and is now SSN-AUKUS, would be seamless with the design and production teams being continuously employed and active.
The additional AUKUS work means that additional staff and facilities are now required and being recruited/built. How that will affect the timing of future build programmes is moot.
Meantime it looks production of the last Astute, HMS Agamemnon, is slipping to the recent fire at the site.
https://www.defenceeye.co.uk/2025/01...edule-rethink/
https://www.rand.org/content/dam/ran...D_MG1128.3.pdf