I have also been having the same issue lately.
I sometimes can't get new WUs after finishing one.
This is on two different Mac laptops, which I have lowered the amount of CPUs assigned, in order to reduce heat and fan noise from this.
As a workaround, I go to FAH Control and CONFIGURE, then delete the SLOTS entry, SAVE and give it a moment.
Then I go back in and add an entry at the default -1 CPU slots and SAVE again.
It will then finally download a new Work Unit. This is consistent about 100% of the time.
Then I can go back in and edit the CPU entry to a lower number if I want.
It would be better without having to do this workaround, of course.
p.s. Remember to always have your registered F@H PASSKEY entered in the IDENTITY tab of CONFIGURE for big (normally) bonus points for your work.
-- folding as proteinmonkey --