The article doesn't say when the satellites that are being lost were launched.
They could be bringing down the earlier versions of satellites intentionally to replace them with new ones.
Yes, the Sun doesn't care when the satellite was launched, but the current orbit of the satellite and drag profile will decide which ones come back down, if not also applied thrust.
It might not choose but we don't know how similar those cohorts are.
It's not the same situation if they already improved the shielding and only old satellites are impacted.
Dunno if it's what happened in this case, but solar flares make the atmosphere bigger* which increases drag on satellites in low Earth orbit.
That said, the satellites have an expected life of 5 years so it's not necessarily a big deal. Their planned constellation is so large that it's dependent on having a nearly continuous churn of replacement satellites.
As one example, IIRC earlier this year they lost some freshly launched satellites in a batch because of a flare, which made the atmosphere expand in density by up to 50% at their altitudes and didn't allow those satellites to point their solar panels at the sun in time.
Starlink sats are launched into a very low orbit and use their ion thrusters to raise into an operational orbit so any which happen to be nonfunctional deorbit very quickly (in the 2 months between this happening and it being reported, many of the involved satellites had already deorbited) and because it maximizes how many they can put up per launch.
So the satellites were lost, as they needed the panel pointed at the sun to sufficiently power the thrusters to overcome drag, but if they moved out of the safe mode orientation of having the solar panel edge point in the direction of motion, the drag would be too high.
Indeed, if you don't have enough delta V to maintain your altitude due to atmospheric drag, increased by solar flares. They've lost them before due to this, an entire batch.