Good news! Unless everyone has already figures it out. If new arrivers have arrived I assume it's because you installed 2.9.0 and tried to open a DWG? It is true that some DWGs work and some don't in 2.9.0 (wierdly?).
Just for reference, the DWGs will not open, but more specifically when trying to drop down the <filename>.dwg in the Catalog to display Polyline, Polygon, Anno...etc. you get the spinning deal and/or an Error. Here is what a functioning DWG dropdown should look like:
As with @wilcow some DWGs opened, others displayed the buggy behavior. Then I simply updated from 2.9.0 to 2.9.2 and the problem was fixed.
SO! 2.9.0 = bad / 2.9.2 = good. So far at least...