Messages starting with Failed HPSS call: n = ::hpss_Read(fd_,buffer,... are HPSS errors. The actual message text can vary but they usually mean that the data is unavailable from tapes for some time.
Most of the times the data is recovered after few minutes. See Retrieve#FailedHPSScall.
If the failure is consistent, please see How to report a Web API issue - Web API FAQ.