The function _updateLastClaimTime() is an internal function which updates the state variable lastClaimTime i.e. Source
This state variable gives us the latest time when the user last claimed his rewards. However, it does not get called from any other function making it completely useless.
Most likely it should have been called from claimRewards() as this is where a user can claim his pending rewards.
However, it has not been done, making the function completely obsolete.
Manual
Consider adding a call to function _updateLastClaimTime() in claimRewards() or directly update the mapping.
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