One possible reason for a delay in the ECHR concluding a judgment after a case is communicated to a respondent State is that the ECHR Registry attempts to broker a "friendly settlement" between the applicant and the State, and this can take considerable time and, of course, is often not successful.
In a friendly settlement, the State admits to having violated the applicant's Convention rights and offers compensation ("just satisfaction") of an amount that the applicant agrees acceptable, and the ECHR agrees that the admission of a violation of rights by the State and its offer of just satisfaction satisfies the protection of human rights.
The ECHR case of Knox v. Italy may or may not be at the stage where the potential of a friendly settlement is being discussed. It is interesting that Italy has agreed to a number of friendly settlements over the past 3 years, according to ECHR statistics. This information on Italy's approach to friendly settlements differs from a post on ISF (in 2014, IIRC) by a pro-guilt poster claiming that Italy never agrees to friendly settlements.
Here's some statistics on friendly settlements, with Italy compared to other western European democracies* of about the same size population or larger:
Friendly settlements before the ECHR by:
Year......2014....2015....2016
Italy.........9.........9.......279
France......4.........1..........2
Germany...2.........0..........4
UK..........12.........1..........0
Source:
http://echr.coe.int/Pages/home.aspx?p=reports&c=
Link: PDF {ECHR} Analysis of Statistics 2016
*Some other countries had a large number of friendly settlements in 2016: Turkey 103; Greece 146; Romania 352; Russia 354; and Ukraine 456.