Most likely you just have a deposit of fine tartrate crystals. If so,
this is a most common thing that will not harm the wine at all. They can
be prevented by chilling the wine before bottling and filtering the
deposit formed out, but there is no need to do so. Tartrate crystals are
very common in some German Rieslings of the highest quality. I have seen
old bottles of German TBA, of the highest quality, that have a huge
amount of tartrate deposit, but this does not harm the wine at all.
There is a slight chance something else has caused the deposit, but I
would not worry about it. Since you have 3 half bottles, perhaps you
could open one soon if you are worried. Just pour the wine carefully to
avoid the solids.