Miners are continuously accepting tasks from the mining pool and returning hash results. However, there is a delay in communication between the miner and the pool’s network. The rate of invalid submissions stemming from network delay is referred to as Rejection Rate. The average rejection rate percentage is 3%. Should you notice the rejection rate fluctuating more than this, the problem may be network instability.
Troubleshooting:
Check the network connection
Check your mining hardware for overheating
Check for firmware issues
Some miners may have a high rejection rate stemming from firmware issues. Should this be the case, consult the manufacturer of the machine for assistance.