Can’t get the front brake right....

Hi Guys,

I rebuild and bled plenty of motorcycle brakes, but the FJS one is not cooperating. I have the left master cylinder sorted, but I can’t get the right hand side to have a solid feel.
(Front calliper is rebuild with new seals)
I tested the brakes and if I brake with the left hand lever only I get it into ABS. But if I brake with the right hand side (only front brake) it had pressure and got into ABS but then lost pressure. I bled again and I cant see bubbles. If I pump a few times it seems to buit pressure again.
Any idea what’s going on? I’m thinking a defective master cylinder but maybe I’m missing something....

Thanks!