Hi @raha_nami thanks for reporting this! Short explanation:
Sending very complex polygons might fail during mesh triangulation. Which is not an “error” technically, the outline of the polygon and the attributes will still be sent, and if you receive it back in QGIS, you will get a proper polygon. The downside is that the other software that don’t support “Polygon” type will not have a backup Mesh to display. Therefore, Revit (which relies on display value Mesh) doesn’t detect it, and doesn’t generate anything in the end.
If the data is not confidential, could you please share the link to your model, so I can explore how the triangulation can be improved? Also a question to you as a user, would you always aim for high-precision outline for the display Mesh (only the Mesh, the actual polygon outline will always be saved with all original data), or would you find acceptable a simplification of the Mesh outline, so that that it can be generated more easily?
Regarding receiving of custom attributes in Revit, you can read more here: Data Transfer QGIS to REVIT , more than geometry - #9 by Sus The short answer is that Speckle will not create new attributes in Revit families automatically, because this is a commonly undesirable behavior for Revit users.
P.S. What versions of each plugin are you using?