It appears that Ettus has updated their PPA again. While trying to instal gqrx on a clean 16.04 system using the MyriadRF guide and repo, I am getting an ABI mismatch (shown below). It appears the affected modules will need to be rebuilt.
GR-UHD detected ABI compatibility mismatch with UHD library.
GR-UHD was build against ABI: 3.10.1,
but UHD library reports ABI: 3.10.2
Suggestion: install an ABI compatible version of UHD,
or rebuild GR-UHD component against this ABI version.