OK, I removed the addpath for all the above packages, then ran 'pkg load
signal', and 'help pwelch' now runs as expected, so this may have put
things in a bit better shape. It will take a bit of time to test/check
it all
properly, but at least it is looking a better than it was.
My guess is that one of the packages you installed is messing up your
paths somehow. Try loading and unloading them, checking signal in
between, until you find the culprit. This is one of the reasons
packages are no longer autoloaded. Some of them can break your Octave.
I'd recommend you to install packages with the -noauto option to
overwrite any autoload settings a package may have. For the ones you
already have installed you can change it with "pkg rebuild -noauto
all". And you can also add a "pkg unload all" on the top of your
.octaverc, and only then, load the packages you need.