Its no cgminer issue but chainminer bundled in Bitfury rig.
Contrary to what you write cgminer in Avalon work without problem

I reported a problem with the Bitfury (chainminer), no cgminer.
Restart stratum proxy in Bitfury rig did not help. Some times reboot RPi solve problem.
cgminer had a 1 out of 4 chance of being effected.
chainminer has been broken forever since it doesn't properly queue work when presented with relatively low difficulty work upon initial connection to Eligius.