There has been a lot of discussion about all this on the Amazon seller forums, with loads of 'conspiracy theories' (some think they are targeting some sellers to get them off the site!); others think Amazon have accidentally messed up their algorithm and are struggling to fix it; others still talk about a 'switch' that turns their sales on and off, as they have seen some weird patters of sales where they get a lot in a morning, and none in an afternoon, or trends that last for a few days.
Personally I think if you read the whole thread on this on that forum, you could end up completely confused because so many people have so many ideas! Something has changed, it must be algorithm related and working out the four corners of it is nigh on impossible. Thus far the only 100% concrete thing I know is this additional keyword change, which let's face it, for those of us who took advantage of the 1,000 characters per field limit, was a pretty tidy problem.
My sales are still down on last year, overall on UK and Germany I am about 15K down which is causing me some cashflow issues (I have a warehouse and staff). I do sell on multiple platforms but the Amazon sites are very important and my income is very bruised right now.