This sounds more like a vacuum drop issue, which would affect the purge valve because there is loss of vacuum and the line itself, it's hose can be plugged, kinked or worse - letting air seep past the check valve and back into the canister / fuel tank - changing the fuel tanks pressure - which can cause that code to re-appear.
So look for and recheck all your vacuum lines - including the ones from the air intake snorkel to the engine - which will share a similar position on the intake.
Now there are two types of ST - one with the turbo and the ST-line type which is normally aspirated (N/A - non-turbo - uses throttle plate and normal air pressure) - so to have this code set usually indicates damage to a line that got whacked by road debris - which may mean Turbo and it's mechanical parts are possibly compromised - which again, changes flow rates and pressure changes in the fuel tank - setting this code.
The Hill Assist is a good strong clue that this is vacuum related - not necessarily a bad turbo, but the tubing in and around the turbo (if it's the one that has it) may be compromised and the built in safeguards are still in place but something in the EVAP line - relating to vacuum - is affected.
How does Hill Assist tie into this? By Vacuum used in the Brake Booster - when the vacuum drops - the booster can't or may not, be able able to provide enough braking - so it turns off hill assist so you are aware of the brakes having less reserve due to the vacuum leak in the system that Hill assist will need to apply (keep up) the pressure in the brake line.
You may also feel a change in the brake pedal when you start the car after it sits overnight. If it's lost all vacuum in the booster - that check valve - the pedal will feel stiff and firm - but start the car, and if you keep pressure on it, the pedal will recover some of it's spongy feel after the engine is started and the booster retrieves vacuum to restore operation. Do not be surprised if the battery and the EPAS (steering control) is also affected for all of this uses electrical power to operate the valves so if the alternator or the battery or both are weak and have long seen better days - time to rethink and replace - before it leaves you stranded.
If that is occurring - several other things will need to be checked - especially under the car, the undercarriage - because there may be some damage and road rash that is affecting the lines under the car from the incident.