How strange! Though I have never observed such a thing (and admittedly I have contaminated some of my bottles of silver in various ways such as gargling, sticking my fingers in, etc.) I think you may be on to something. I cannot imagine any kind of bacteria growing in properly made colloidal/ionic silver.
Over time, ionic silver tends to agglomerate and precipitate out to the bottom of the container - and it happens with even the best mostly true Colloidal Silver products, although to a very, very small degree in my experience. I have seen Colloidal Silver that is years old with almost no particulate matter on the bottom of the container.
One exception is if the silver solution is exposed to very cold temperatures. That will surely cause considerable agglomeration.
BTW, the mention of 10 PPM - which is good - makes me really shake my head in dismay when I see the advertisements that pop up here these days for "silver atoms", "atomic silver" and "high PPM (up to 18,000 PPM) Colloidal Silver ". What rubbish - and I hate to see our members exposed to such false advertisements! My two cents . . .