1st thing to check is the hydraulic circuit. Chances are you have a leaking master or slave & or air in the system.
Failing that & the push is correct, a similar result can come from a loose or incorrectly fitted clutch cover/diapragm.
In this case the box needs to come out.
On inspection if the clutch is ok, your next inspection is inside the box.
That being the three M6 x 1.0mm bolts (10mm head) retaining the interlock lower plate are likely loose together with the 2 M6 bolts retaining the reverse selector.
Follow oem manual for box disassembly, re-assembly procedure