This is a tricky one and, from personal experience, probably the hardest thing to calibrate. To answer the question, this should NOT be happening with regular PLA, as in your example with the blue filament. There is something seriously off with the calibration. Did you use the default Bambu Profiles for PLA Basic?
Another, less likely, factor could be incorrect temperatures being read by the thermistor underneath the silicone sock. When was the last time you removed the sock and scraped away any buildup? When was the last time you inspected the sock and the nozzle tip for accumulation? This isn’t normally part of routine maintenance, but when I had this problem and couldn’t figure it out, I changed the nozzle, thinking that was the issue, only to discover buildup under the silicone sock. I scraped it away with my fingernail, put on a new sock, and tested it. The stringing went away. Since that’s the only thing I changed, I assumed the accumulated filament was affecting pressure advance or the temperature reporting back to the MC card.
Of you haven’t already done so, try using the Orca String Hell model. That name is an understatement, it can’t be perfectly calibrated at least with my humble skills. But if you get close, you can really improve stringing.
Here’s a tip, cut the model and only use 1/3rd. It will save you a lot of time, otherwise, you will be waiting 10 minutes. The 1/3rd model is good enough.
