I am not being able to grab any tasks from YAFU. Other BOINC projects are working fine. On the server status page I can see that there are tasks available, but for some reason my client is not being able to grab them.
Log messages:

24/02/2019 12:21:10 | yafu | Resetting project
24/02/2019 12:21:15 | yafu | Master file download succeeded
24/02/2019 12:21:20 | yafu | Sending scheduler request: To fetch work.
24/02/2019 12:21:20 | yafu | Requesting new tasks for CPU
24/02/2019 12:21:23 | yafu | Scheduler request completed: got 0 new tasks
24/02/2019 12:21:23 | yafu | No tasks sent
24/02/2019 12:21:23 | yafu | No tasks are available for YAFU
24/02/2019 12:21:23 | yafu | No tasks are available for YAFU for small composites

Does anyone know what may be causing this? Thanks.

All your hosts have no more than 6 cpu. So you get only yafu and yafu-small workunits.
Those both queues are very often empty.

Thanks. It seems to have to do with computing preferences, which, when set to use only one core (eg. 25% on a 4 core cpu), makes it so that no yafu tasks run, even after setting yafu as using one cpu on app_config. I have fixed it by setting computing preferences back to use 100% of cpu cores.