Very near GAIA DR2 sources - has Proxima Centauri been dethroned? I made an extract of GAIA DR2 data for parallaxes greater than 500mas. Surprisingly I see a very significant number of sources with parallax greater that 1000, making them much closer than Proxima. This should lead to excited newspaper headlines, but i haven't seen those yet... Am I missing something?

You can see my extract of data here:

https://gist.github.com/agnes1/1492e94b5e9c0ef71f6ae7944964b666

Some GAIA source_id rows to look at include:

4039503676370417664

4042946384760661504

4042338732771057920

4046453826887613696

But there are many more. The closest source I find is 4062964299525805952 with  parallax of 1851mas. It has a phot_g_mean_mag of 19.63355... Would I be right in assuming this is a brown dwarf?

Another thing I note is that there is a surge of vmag 19/20 sources within 10 parsecs. These are obviously so faint GAIA doe not detect similar sources beyond 10 parsecs. To give some numbers I count 1722 sources (most mag 19/20) within 10 parsecs and only 606 sources in a shell of equal volume beyond that. Again, would these all be (a very large number of) brown dwarfs?
These are spurious data points. They are likely genuine objects, but the parallax value is incorrect. There are a small number of these in the Gaia data set. 

There are 59 object with a parallax greater than Proxima Centuri. These don't represent genuine objects, instead they are when two sources are closely aligned (within about 0.2 arcsec). Most of these are found in the milky way, where there are lots of stars close together.

See
https://www.cosmos.esa.int/web/gaia/forum#!/thread/1688565/1688576

And section 9 of https://arxiv.org/pdf/1804.09365.pdf