A bit more information to get better support would be helpful.
You mentioned that you printed with this PLA before - on the X1C or another printer?
Which profiles for the filament you are using? What PLA (Brand)? Stock settings or modified profiles?
I recognize that Bambu invests a good amount of resources to make the UE as flawless as possible, but there are still settings that seems better deviating from stock. In my opinion it looks a bit of a combination of temperature / cooling and speed which shows effect only after some time of printing - as during heat up etc there is still a good amount of flow available.
As soon as more information is available, we can help better.
For future references and with almost a year of experience of the X1C one of the first things I always do with a new filament brand (and before I commit to purchase more) is to perform an volumetric flow test.
This shows relatively fast if an high throughput / melding and layer adhesion can be achieved by the filament. Nothing is worse than to have a fast machine only to be let down by bad filament. And it sometimes is only a difference of 2$ per kg of a spool to have a fast print or a slow or failed print