If you do an lspv or an lsvg -l thevg and the commands return nothing .. it probably means that the volume group is locked.
Had an issue today where it just was not returning any errors and had no output. Turned out there was a disk operation error, and it didn't tell me in the error report that it locked the volume group. A simple fix:
chvg -u thevg
Fixed all my problems. :)