Comment 18 for bug 2025565

My solution:

So - in desparation, before doing a full re-install, I 'tried a few things'

This seems to have got me free of what looks like some sort of circular dependancy

My actions were

 2004 sudo dpkg --purge libnvidia-gl-535:i386
 2006 sudo dpkg --purge libnvidia-gl-535

One of the two previous commands may be redundant

 2009 sudo apt install libnvidia-gl-535

This did an awful lot of work, installing missing stuff

 2010 sudo apt-get check

Came back clean

Obviously this is just me groping in the dark, but it may help someone

rgds

Ian B.