Unfortunately I'm not entirely convinced any sort of 'fix' was actually implemented. If what Remy_5 indicated earlier is true regarding nav having it's 3rd birthday doesn't the PoS block reward get cut in half at that point? That coupled with the recent network weight increase might explain the major delta we are all experiencing on staked wallets at this point.
Bingo! This is main reason.
Since block 2102401, what was assumed to be the first block of the third year,
it began operating a new rate of reward, which is now only 5%.
So the value of the stake grows much, much more slowly than before and in
a more linear way. And that in itself is enough to justify your observations.
About the fix, if you have not changed your code, or updated program of wallet,
then obviously there is no fix in action.
As I see, the secondary triggers reasons, there are still all, the little group of
addresses that produce blocks in the future, continue in their slip forward.
(It was the so-called group A of the little experiment a few weeks ago).
Other indirect reasons, are internal to the code and are somewhat common to
all POS coins.
The substantial improvement that's been around the 2015/10/10, is due to some
circumstances "environmental".
Our "whale", has probably restarted his wallet, and its new time-offset is
now very close to zero, this has as it were, shifted the center of mass of
the times in a more favorable position.
In addition, after the re-adjustment of its groups of coins after the change
of address, the whale has returned to produce blocks with great frequency,
and thanks to its "weight", and the low Diff, he has produced very long chains
of consecutive blocks, also 15 blocks in a row.
Normally this would be very unpleasant, but in this case, the blocks produced
from the same source did not have large changes of time back and forth,
and not to have negative intervals gave way at PosDiff to rise a little,
pushing the block interval to 12-15 second circa, finally.
Instead, the rise of PosDiff of the last few hours, is another indirect effect
of the change of interest.
There is more to say, for example on how to re-optimize the size of the blocks,
but it's late and it's better to know first what are the intentions of the DevTeam.
Happy New Year!