The pvestatd is waiting for responses from PBS which was pretty slow earlier. We just tuned the ZFS filesystem a bit with a 'special' device and upgraded to 0.8-19 which seems to have improved webserver-responses a bit.
Yes, the singlethreadedness of pvestatd is a problem that causes lots of confusion. I'll create a PVE-bug for that.
As far as PBS is concerned, I see no signs of issues on that side. Logging continues as normal and statistics do not show storage or CPU to be very busy. Performance of the PBS seems to need improvement somewhere, but I cannot see how many clients are connected, which is kind of a nice feature to have. I'll create a feature request for that.