[tor-relays] tor-arm bandwidth state file -xxxx seconds is missing?

[SuperSluether]

Found this error when checking my relay today:

ARM_NOTICE Read the last day of bandwidth history from the state file 
(-xxxx seconds is missing)

Every time I start arm, the -xxx seconds missing is different. The 
bandwidth graph is also stuck, but real-time data is still shown.

Is this a problem with Tor, or with Arm? Anyone know a fix?