My character is logged in, all the materials are in the storage, the workers have full stamina, but still sometimes they don't auto repeat their last task in the workshop.
I use "repeat all" one day and the small "repeat" button near every worker another day, but i still get some workers not auto repeating the last task.
It happens when i am actively playing, and it happens when i have long afk time.
The guide doesn't have any information on how many times a worker can repeat their task. It says 50.000 times on nodes, but it says nothing about limits on workshop.
Am i missing something? Am i doing something wrong?

Not sure about it. I use the node to set the number of tasks.  For example; if I am doing saddles and I estimate the materials to max of 4, I set it to 4.  If my goblin in Velia is farming potatoes, I normally set it to 10 because of the low goblin stamina.  They do complete tasks even when you are offline.  If you set it to 50,000 there is no way the stamina will last or the materials.  One or the other will run out and they will give up and go home. 

I do know, the nickname function is glitchy.  I will rename them just have them back to their generic names, when they do server maintenance on Wednesday morning.  I no longer bother giving them goofy names no one else can see. 

Have fun!

nodes are fine, my problem is the workshop. i am crafting the forest pathwagon in Grana, but often i leave the pc running and when i come back i see some workers doing nothing and their stamina almost full. it is disappointing and i can't understand why it happens

Wagons and ships are crafted differently than other items. They have multiple parts, that needs to be built one by one, and you can't just auto repeat it untill it's done.

like CatDK said  forest path and the ships are unique in how theyre made

so like the 2000 pieces of image  if u set a worker to do that 100 times   another worker 1900 times  the game registers that as all 2000 crafts and wont let u tell more to work

iirc when u tell a worker to auto repeat  the game tells it to craft max allowed amount of times or until its stam ends depending on how often u feed  so forest path itll kinda derp out as the game tells 1 worker to do it all

best bet is to manualy restart each time with 5 to 10 each

The last reason that I can think of is that if your wagon is 498 / 500 of certain materials and one of your minion is tasked to do 2, then you can't assign anyone else to complete it since it would go over the limit. A more realistic example would be if you have 920 / 1000 materials completed and you have 10 workers ready to work. You assign 5 of them to do it 10 times (let's say) and that's already 50 points. You're at 970 / 1000 so far. Now you assign 3 more workers to do it 10 times and it's now 1000 / 1000. Any other minions you want to assign won't work even though they technically could if you would have given other workers less work.