This issue may be caused by the low Available Memory and resources for Report Server Applications.
- Available Memory.
As we know, when the report dataset query being executed, it will spend much memory source. If the available memory size is too low, after few times, the Report Server will redistribute these resources to other reports, so please increase the size of the Available Memory.
Configuring Available Memory for Report Server Applications.
- System resources.
Although the Available Memory is big enough, if the system resources is limited, after few times, system will recycle the resource from the report then redistributing the resource to other applications. Please try to free sources by disabling the unimportant startup items, then rebooting the machine.
Please try to test previous suggestion in your project. If the issue still exists, please feel free let me know.