All you have to do is make the slotted hole after making the thread.
Indeed, you add more material after the oblong.
You need to be able to just move the oblong function without redoing the entire slotted hole.
Kind regards
PS:
[Off-topic] it seems to me that there are one or two defects on your thread and why not use the function provided for this instead of doing a scan. ;-) It all depends on your version but it has existed since 2017 it seems to me but safe in 2018 and beyond
Agree with @Zozo_mp. Your oblong function (removal of material through everything in 2 directions if you sketch in the middle of the axis) must be done after your scan or your "Thread" function. Since you are in SW2019, I have quickly given you an example.
But do you really need to represent the shape of your thread? This complicates your 3D model. A simple thread representation is usually sufficient!
Indeed, I completely agree with both of you, @jmsavoyat and @Zozo_mp, only this part does not and will not be part of a mechanical assembly but screws into pre-perforated PU, so has the function of self-tapping the PU in a way. For this I need a sweep along a helical line in order to be able to create my own thread shape (with sharp edges).
And fortunately, if the material removal function (slotted hole) is after the thread assist function, everything is fine, but if the material removal function (slotted hole) and after the scan function, here SW19 does not want to build due to the geometry (see image 1). My question was about this specific problem.
And if I have searched correctly, it is impossible to modify the thread profile given by the thread assist so I cannot use the thread assist function.
Thank you for your help, and I hope you have the answer to my question.