Validators cannot start due to existing lock file
This may occur, for example, in the event of a power failure—when the staking node powers back on, validators cannot start due to existing lock files.
Lock files can be removed with a use of Remove Lock files util.
Stucked Execution/TekuBeacon client
If a any client got stucked, you can simply restart them.
sudo systemctl restart ExecutionService
sudo systemctl restart tekubeacon
This (and many others) can be also automated through Teku Beacon Log Monitor service.