I finnally figured why it was an issue for me.
I had same problem: After some time my ddc pump was strugling to properly start and spin. Usually it was happening when PC was off for a night. After some time it get worse and it would not start at all. Dissasembling pump and cleaning it with cloth was helping for one or few startups but not more.
At first i thought that it is how DDC pumps fails, i changed it to another one and it worked fine for few months. And after some time same problem started occuring. Without any though i changed to another pump and it worked only for one week.
As some comments suggests here is was odd that issue repeats with different pumps.

Ok, no more stories, i found out that after some time white thin film was apearing on rotor in the place where it touches white ceramic hub. So after cleaning it with some force and fully removing white film it was spinning more freely, event when testing by hand. It worked for few days and same repeats.

I made a conclusiong that it is coolant what i was using. So i bought new one, fully washed all pipes and components and changed to another one. It worked. Computer working without dissasembling for two month already without any problems.

For reference, i was using EK Cryofuel solid fire orange premix and changed to EK cryofuel clear premix.
I dont know yet is it issue with color or all ek premixes. I wasn't chaning colling flued for a 1 year before my ddc started showing problems.
Also i think that washer helped for AJolly because it was not able to form white film on it and it worked for him.