Photos didn't upload to iCloud

Hello, I am with iMac 21,5", Late 2013 and iPhone 6 plus 64 gb, iOS 8.4

I turned on my iCloud Photo Library with 500 GB. I have about 40 000 pictures and 200 videos.

I have started to upload everything from my iMac to iCloud. Meanwhile I deleted everything from my iPhone and after that I started iCloud Photo Library on my iPhone with function Optimize iPhone Storage ON.

My iMac uploaded approximately 25 000 photos and 90 videos and stopped. It was done for 2 days and since then (may be more then 15 days there is nothing else were upload). Meanwhile everything was synchronized on my iPhone. I start to make pictures with my iPhone but now everything stay only on my iPhone. Nothing is upload neither from my iPhone nor my iMac.

So my question is why everything stops?

I have enough space (everything takes around 300 GB) so I have free 200 GB more.

But since 2 weeks everything new stay only on my iPhone if I take pictures with it, or on my iMac if I import pictures there.

What have I done wrong? And why everything stops? I can see on settings that my iPhone is trying to upload the new photos but it stops all the time and never upload anything else.