Hi,
I took a look at the logs of the assset 3649084 and it looks like the error for the invalid file states: Missing spatial reference system (srsName)
I do see the CRS under the CityObjectMember tag. I think you are running into an instance where ion isn’t detecting the SRS because it isn’t at the top level within the CityModel tag. I would suggest trying something like this: Citygml to 3d tiles - #4 by a.scalas
If that works, I will create an issue and bump the team to look at how to fix it
Thanks,
Ankit