Looks like the tarball for hplip was changed in-place again. It's been this way for a few days, and since it doesn't seem to have been reported yet, I figured I should do it.
building /gnu/store/5a07ajq8zkhblayhzn6z94nj8cgad406-hplip-3.20.6.tar.gz.drv... downloading from http://downloads.sourceforge.net/project/hplip/hplip/3.20.6/hplip-3.20.6.tar.gz ... -sha256 hash mismatch for /gnu/store/ha65zsjdid82snj1w2c9mykl8iavwkww-hplip-3.20.6.tar.gz: expected hash: 0rmk7i28mb0q66i5l9d0fq2j23dkhz5gx5g2xvi16ga0dnprcilp actual hash: 083w58wpvvm6sir6rf5dwx3r0rman9sv1zpl26chl0a88crjsjy6 hash mismatch for store item '/gnu/store/ha65zsjdid82snj1w2c9mykl8iavwkww-hplip-3.20.6.tar.gz' build of /gnu/store/5a07ajq8zkhblayhzn6z94nj8cgad406-hplip-3.20.6.tar.gz.drv failed
