Probably caused by an (earlier) failed scheduler contact that actually got through to the scheduler after Boinc managed to complete a later scheduler contact,
and because the contact numbers came in the wrong order, the scheduler abandons all the work (server side only),
leaving the host with a lot of abandoned work that is pointless to complete.

Reset the project on that host, you'll get only your unabandoned work resent, at present you only have 31 in progress tasks.

Claggy