19.5 hours and still more than an hour to finish. Is it normal?

Yep that's normal. I've seen as fast as 12 hrs and as slow as 30 across my computers.

Now i see some units that after more than 8, 13 and 16 hours are just around the 10%. Is this still normal? The CPU is always the same.

Did you add any new projects? If you had one that utilizes all of your PCs AMD GPUs and their tasks can run on your CPUs onboard graphics, that would seriously inhibit you CPU performance.

I'm also running Amicable Numbers with 2 GPUs but it just takes 0.184 CPU each.

It's not accidentally running a third is it? Otherwise I've heard of tasks either being very long or hanging but I haven't experienced it myself.

8 cores and 8 taks. 2 GPUs and 2 tasks. Nothing else is running.

Well you can either wait and see if there finish or abort and try again, or wait for someone more qualified to answer

They finish successfully but the needed time is now longer than the first WAs. To be precise, now is shorter than yesterday but such continuous fluctuation is weird.

They do vary, even on the same system. Like 20hr to 30 hour depending on he contents of the task. The tasks aren't uniform in length and the credit is adjusted accordingly

Oh i got it then. It's weird because they're usually the same in other projects. Thank you for this clarification.