There are many hidden bugs and problems at Revit if we import a dwg file without cleaning (such as purge, explode, flatten)
Before importing dwg file Revit should have an option to purge and flatten and other clean up jobs which are listed at here.
for example, I imported a dwg Survey file it has many problems such as:
1- drawing doesn't flatten and vertical Cad file shows at the elevation and sections!
2- after importing without purge some of the dwg file's text boxes have font style problems (see below image)
3-some of the cad blocks after importing change to weird shaped (see below image)
Original cad drawing is like below

but after importing to Revit it shows like this

for more information see related topics
https://forums.autodesk.com/t5/revit-architecture-forum/dwg-files-has-weird-text-after-importing-in-...
https://forums.autodesk.com/t5/revit-architecture-forum/at-hide-line-visual-style-revit-shows-the-hi...