in counterstrike people had to manually build the arches to avoid this very issue long time ago, i still do sometimes out of habit even if generating an arch have its own benefits like adjusting the curve and width height etc where it all resizes, still spend 10 mins on it and use in entire map if you want!
Personally i recommend pressing
S for surface inspector and messing with the
Natural or
Lightmap buttons
Going back & forth between the options can actually put all the textures in place for you no effort required...given the lightmap looks good unlike in this case where i just wanted to give you and other mapper an idea of what could solve the problem quickly.
this is the best way i find to align any surface that is a mix of both patch and brush. Thats why scrolling can have negative impact since it start going in different directions, best way to reset a texture alignment is picking a new texture or going back to the one you had then doing the steps i showed you with
natural and
lightmap________________________________________________________________________________________________________________
here is just a bad example of what i first meant but that way there wont be any seem between textures if you cannot figure out the way i did above.Here i needed a very flat curve in this scenario but could not be bothered with patches so i made an exception and used a couple brushes