...humm; just a thought; some simple stuff to check, that you probably already did; did you adjust or turn off the hydraulic control valve? ... under the seat on my YM180D; should always be open full. 1+ clean strainer, and change hydraulic filter; how much dirt, debris came off and out on filter and in fluid, (ie whats left at the bottom of the oil bucket after letting settle and pouring off fluid in used containers to dispose of oil).
How much Hyd fluid did you put in / replace?; there conflicting info on quantity on some tractors I remember it was about 18L on the YM180D; because its a shared system its more than you'd think.
Also pinched / bent hyd hose? Or were the lines moved around on the control lever?