First of all thank you for trying “locallab”
First of all, admit that this case is particularly delicate, a mix of light sources, huge overexposure after +1 in "exposure"
Actually we see artefacts appear in the boundary intermediate area between the area with L = 100 and the colored area where L is less than 100.
I looked in the code of “locallab exposure” (curves, algorithm, …) and I did not find. This does not prove that there are no errors.
I tested “graduated filter” and it works well…
So why these differences in behavior ?
Graduated filter is before “Lab conversion”, and work in RGB mode, but before “exposure” (as white balance, fattal, Retinex…)
Locallab, works in “Lab” and after rgb mode, after “exposure”
This explain the differences of behavior. With “locallab exposure” it is quasi impossible to retrieve goods datas, because all is superior at L=100, all is burned.
I think, I am not sure, because Color management is a complex thing, that these artifacts are due to “out of gamut” for some colors (beyond Prophoto), when reducing Luminance, and this artifacts cannot be retrieve by “avoid color shift” - because this appears after creating artifacts and are not due to Locallab algo.
Consequently, for this image I tried 2 things :
with the branch “autowblocal”, and “Local WB”, I change the temperture, of the overexposed area (the one you use a flash), then I exported a TIF, then I open the TIF and apply “locallab” correction, no artifacts
without “autowblocal”, I change the settings of General White Balance - actually 5300K -, for example increase “temperature” about 5900K (you can also change “tint” or “equalizer”), artifacts disappears.
I do not say that there is nothing to do, but:
a) check with others developpers, during future work on “locallab” that I did not make coding errors
b) if these cases arise (they must be rare), it will be necessary to combine the actions (White Balance, WB local, locallab), or create a module in RGB mode (as for WB local, multi graduated filter, etc.)