Webhdfs internally acquires a token that will be used for DN-based operations. The token renewer in common will try to renew that token. If a renewal fails for any reason, it will try to get another token. If that fails, it gives up and the token webhdfs holds will soon expire.
A transient network outage or a restart of the NN may cause webhdfs to be left holding an expired token, effectively rendering webhdfs useless. This is fatal for daemons.