I understand your meaning here, Russia did not shift to tactical, targeting and fire control radars, or select which type of missiles to use against any of the incoming missiles, but their observational capabilities were always on. The Russians chose to not use the S-400 System, they did not turn it off.
Likely, the Coalition were hoping that they would spin up and fire some S-400 assets.
The S-400 is only effective against airborne targets, and the UK aircraft were the only manned airborne targets, they took off from Grecian Southern Cyprus, launched their 8 or so Stormshadow cruise missiles, and returned to base.
The maximum S-400 anti aircraft range is about 250 miles (anti missile range, 90 miles), so the Brits were safe at 80% of S-400 range and could see them coming from far off.
Syria's older systems could knock down Stormshadows, so using rare S-400 assets would reveal more about S-400 than Russia wants to, short of protecting Russian flagged troops.
There were a couple B-1's that rippled off some missiles too.
As I’m sure you’re aware, but many aren’t, not every TLAM is the same. Additionally, there’s some interesting physics at play when confronting a stream raid.