It is a long standing issue and problemā¦
Whenever layer times go out of whack wall do as well.
A lot can be compensated for through a good (manual) calibration of filaments, speeds and temps but not all.
In your particular case it seems that your extrusion goes out of whack because the filament is being unloaded AND the print has far time too cool down while the supports are printed and those filament changes happen.
A bit like first layer elephant foot combined with softer than average filament coming out of the nozzle for a little while.
It just changes how the filament spreads out and behaves.
In theory the PA calibrations should take care of this but Bambu does not have anything implemented to deal with the unavoidable things that come with filament changes during a print.
Hereās what I used to minimise the issues >
Proper flow ratio calibration after the best print temp was established.
Means not being shy to create filament profiles for those lower layer heights.
Also means ACTUALLY finding the best nozzle temp range for the speeds in question.
Let me explain this part as it seems to still confuse a lot of peopleā¦
You need a minimum nozzle temp in order to get a good layer bond and canāt go above a certain nozzle temp without risking the filament getting running during slow print moves.
The consistency changes with the temperature AND the time the filament spend in the heating chamber.
In other words, the slower you go the more time for the filament in the chamber to change properties.
Ideal is a temp that still gives proper layer bonds at the max print speed you plan to use in that profile while NOT creating a goo mess on top of fine or pointy details.
Check the cooling and fan speed options here 
The flow ration calibration seems straight forward in the Bambu world.
Print the patches, do it again for the second round and all is perfect - if your eyesight is as perfect as your judgement of the surfaces of these patches.
You see the issue here, interpretation and of course the fact that some filaments/colours are very hard to check this way.
Then there is the issue of accuracyā¦
Letās say you got the standard flow ration calibration dine and the prints look fine.
Then you want to print this figurine in 0.08mmlayers it comes out looking terrible - what happened??
Volume happened
Letās go with the standard 0.42mm wall width and a layer height of 0.2mm.
Gives us a volume of 0,027708847173 in cubic millimetresā¦
NOT really much at allā¦
At 0.8mm layers however we only extrude 0,0110835388692 - less than half the volume.
I leave it up you you to work out how this translates when your flow ratio is off by 10% or soā¦
Hence me doing a manual calibration if the Bambu patches are too inconclusive and also when my test prints show I need to adjust the flow ratio for lower layer heights.
Sadly not always does a manual flow ratio calibration that gives perfect results at 0.08mm layers work as goo for 0.2mm layers.
Flow rates do affect filament propertiesā¦
With the above sorted we are left with possible tweaks of the print settings.
The best tweak is also the worst one.
Imagine you want to clean and detail you car > What gives you the better result?
You rushing through it in an hour or you taking an hour longer ?
Same for your prints.
Those wall issues with supports, opening or gaps in walls or just having layers with much lower layer times for a while all go way (almost fully) at low print speeds.
To be precise here > The print quality is best if your layer times and print moves are consistent.
At those slow speeds a lower nozzle temp can be used which further increases constancy.
Of course it can also mean that a 3 hour print then takes 7 or more hoursā¦
Try to find an acceptable balance for those vital printsā¦
Ok, what about other settings?
Scarf seams are supposed to make seams go disappear but if your normal seams look terrible than using a scarf wonāt help.
You need to tune those seam setting, the gap percentage and such.
And like it or not - it your filament isnāt calibrated you now already start to compensate for issues you shouldnāt have and might create more headaches later on.
All starts and ends with a good filament calibration, donāt ever think otherwise
A good compromise is possible if you play a bit with the wall widths.
For strong walls you can use, lets say 5 wall loops, giving you about 2.22mm on average.
But with inner walls of 0.65mm you get 1.72mm walls with just 3 wall loops - a massive reduction in print time.
But it has to match the model needs!
Take a star pattern - the inner corners would probably start to suffer from bulging while you might have gaps between the loops at the tips.
For rounded objects with slopes and overhangs this can help a lot to avoid extrusion related wall issues.
The other way around, using more and thin inner wall loops and maybe a slightly wider outer wall can really help with pesky overhangs and details of the model that otherwise create these outstanding wall āfeaturesā.
This āSmooth speed discontinuity areaā thing is also worth checking out.
In lame words it works together with the PA settings (the k-factor you hopefully calibrated well) to make sure the melting chamber is not subjected to extreme pressure changes.
It also helps to improve the detail quality where the acceleration setting would otherwise just make the head rush through the area.
Lowering this value to 125 or even below 100 for complex prints can provide a real improvement on print quality.
But it can increase the print time slightly.
Despite being a total waste a prime tower of matching size and place close to the model and often let the too soft filament get used up so once it continues on the actual print the filament quality is far more consistent.
It is a hit and miss game though due to the waste amount and fact that still wonāt help where you have windows in a wall or such.
Last but not least I would like to mention that using a high flow hotend did make a massive difference for me.
It is not so much the possible speed increases it is more the fact that these hotends are far less restrictive.
And THAT means they donāt suffer from the overall higher chamber pressures of the Bambu hotends.
