I hate to the master of the obvious here, but if your joints have been done the same way for years with the same fillers for an equal number of years with no problem, Then your only other variable is something new. Without a proper etch and magnification I can't tell much from the pictures, but it seems to me since since all three processes are experiencing the same problem in greater or lesser degrees, the only thing left would be the base material. Suggest cutting three grooves into a single plate of that material spaced enough to avoid interactions of HAZ and running SAW, FCAW, and GMAW in them then cutting and proper macro. If it's the base material, it will be in all three. If it was one or the other processes it would only show up in that process.
My two cents worth,
Gerald