It will help to be more precise. Itead sell two different Zigbee dongles based on different radio chips (using different Zigbee stacks with different firmware), the Sonoff ZBDongle-P based on Texas Instruments CC2652P and the Sonoff ZBDongle-E based on Silicon Labs EFR32MG21.
What exact firmware version are you using?
FYI, most common problem symtoms are due to Zigbee network that is not optimized or user error in the setup/configuration, which is why it a generally a good idea to make sure you are already following all the best practices before as it makes troubleshooting much harder if you are not, see → Zigbee networks: how to guide for avoiding interference and optimize for getting better range + coverage
Not a good idea to assume that you are already following all best practices when most other people are not.