Nautilus does not launch in Ubuntu 19.04
In my 18.04 setup I had problems with tracker causing the same issue, nautilus not launching, then it worked by killing tracker, but now that did not work either.
What did work, was resetting tracker. I performed a hard reset, you might try a soft reset, maybe it could work too, I didn't test, since it got fixed by the hard reset. Sidenote: I disabled search in files.
tracker hard reset in terminal :
tracker reset -r
tracker soft reset :
tracker reset -e