I'll take a stab at it..... (Wild as__d calculated guess).
From what your saying, you think some pressure is trapped in the master, hose, or slave which is preventing the clutch from moving.
To troubleshoot it, isolate the sections.
1. Operate the clutch until it reaches the point that it does not return. (90%)
2. Loosen the brake line at the slave cylinder.
If the clutch extends, the blockage is in the master or hose.
If the clutch reamains in the 90% position,. the slave has a problem.
3. (Repeat) Operate the clutch until it reaches the point that it does not return. (90%)
4. Loosen the brake line at the master cylinder.
If the clutch extends, the blockage is in the master.
If the clucth reamins in the 90% position, the hose has a problem.
In all cases, watch the fluid that comes out. At some point you will see increased flow due to the slight pressure being released.
Ride safe, Ted