Hello Geronimo 
The fact that after redesigning the report you got a database log on fail, indicates that this is a database / datasource issue. To me, the behavior indicates that the report engine is finding some sort of an incompatibiity or change in the datasource that it does not understand. Or, the datasource is not available when the engine needs to retrieve the data. See if enabling the option, "Verify on first refresh" will help. This will help if the detected inconsistency in the datasource is minor.
As far as suspecting a CR bug. The question that would need to be answered is; why is it happening in this case only? E.g.; I know I'd never be able to reproduce the issue.
To that end, an interesting test may be the following;
Run the report until it fails
Leave the app running
As soon as the report fails, create an xml off of the datasource
Open the report in the CR designer and point it at the above xml. See this blog on the details of how to.
It will be interesting to see how the report work when going against the xml - my suspicion is that it will either not work at all, or that yo will get a field mapping dialog - confirming there is something in the datasource the engine does not understand.
- Ludel