This is “normal” with Black, it’s the pigments setting at the bottom of the tank. When I was still using Black I had to spend at least 30min stirring the resin in the tank to get a decent homogeneity unless I was using the resin at least every couple of days in which case 5 min was enough. I can’t even imagine the amount of settling that is going on in the cartridges, and I also did spend a long time before each print thoroughly shaking the cartridges.
Due to this issue and maybe others I have had a very bad time with this resin and have since switched to Grey when I need a Standard resin part, which I will paint in black when needed.
This also happens with the White resin to a somewhat lesser extent.
One diagnostic tool for you would be to print with Grey or Clear, and see if the results are similar, in which case I’d contact support to troubleshoot the printer.